Imagine scanning a product barcode at a supermarket.
The scanner reads the identifier.
The system looks up that identifier in its database.
But instead of finding one clearly defined product, the same identifier is associated with two completely different products.
What happens then?
The system may not know which product the identifier is actually supposed to represent.
This is why unique product identification is one of the foundations of modern retail, e-commerce, inventory management and product verification.
GS1 states that each different product should have its own unique GTIN, and that one GS1 GTIN can only be assigned to one product.
🆔 What Is a Product Identifier?
A product identifier is a number or code used to distinguish a product from other products.
Examples include:
- GTIN
- EAN
- UPC
- Internal product IDs
- SKU numbers
- Serialised identifiers
- Private identification numbers
The exact structure and rules depend on the identification system.
For example, within the GS1 system, a GTIN is designed to uniquely identify a trade item. GS1 explains that different products are assigned separate GTINs.
🔢 What Does “Unique” Actually Mean?
Unique does not mean that the identifier appears only once on the physical products.
This is an important distinction.
Suppose a company manufactures 1,00,000 identical bottles of the same product.
All 1,00,000 bottles can legitimately carry the same product identifier when they represent the same defined product.
GS1 explains that one GTIN can be used unlimited times on the same product.
Example
Product A — 500 ml Orange Juice
GTIN:
8901234567890
The same GTIN may appear on:
- Bottle 1
- Bottle 2
- Bottle 3
- Bottle 4
- …
- Bottle 100,000
That is not a duplicate identifier problem.
They are all instances of the same product.
⚠️ When Does the Real Problem Occur?
The problem occurs when:
Product A → Identifier 123456789
and
Product B → Identifier 123456789
while Product A and Product B are actually different products that should have separate identities.
Now the same identifier is being used to represent two different product records.
That can create serious data problems.
GS1 explicitly states that a GS1 GTIN cannot be reused for another product once assigned.
🧃 A Simple Example
Imagine these two products:
Product A
Brand: ABC
Product: Mango Juice
Size: 500 ml
Identifier:
1234567890123
Product B
Brand: XYZ
Product: Apple Juice
Size: 1 litre
Identifier:
1234567890123
Both products are now using the same identifier.
A scanner cannot determine from the identifier alone which of these two different product records was intended.
That’s where the problem begins.
🛒 What Can Happen at a Retail Store?
Retail systems often use product identifiers to retrieve product information.
A simplified process looks like:
Scan Barcode
⬇️
Read Identifier
⬇️
Search Database
⬇️
Find Product
⬇️
Retrieve Price / Product Information
⬇️
Complete Transaction
GTINs are specifically designed to allow products to be looked up in databases for functions such as price lookup, sales recording, delivery confirmation and order identification.
If one identifier incorrectly points to two different products, the database lookup can become ambiguous or incorrect.
💰 Problem 1: Incorrect Price
Suppose:
Product A = ₹100
and
Product B = ₹250
But both use the same identifier.
A checkout system may retrieve the wrong product record.
The result could be:
Product B scanned → Product A’s price displayed
or another form of incorrect data, depending on how the retailer’s system handles the conflict.
This is one reason why product identity must remain consistent throughout the system.
📦 Problem 2: Inventory Errors
Inventory systems depend heavily on product identification.
Suppose a warehouse has:
Product A — 500 units
and
Product B — 300 units
If both products are incorrectly represented by the same identifier, the system may have difficulty distinguishing their inventory.
Instead of:
A = 500
B = 300
the database could effectively see:
Identifier X = 800
That can affect:
- Stock counts
- Reordering
- Warehouse picking
- Goods receiving
- Sales reports
- Inventory valuation
🚚 Problem 3: Shipping and Fulfilment Errors
Imagine an online customer orders:
Blue T-shirt — Size M
But the same identifier has also been associated with:
Blue T-shirt — Size L
The fulfilment system needs a reliable way to distinguish them.
GS1 specifically explains that product variations such as size and colour require their own unique GTINs so that marketplaces and supply-chain systems can distinguish what the customer ordered.
🛍️ Problem 4: E-commerce Listing Confusion
Online marketplaces depend on product identifiers to organize catalogue information.
Consider:
Identifier X
→ Product A
But another seller submits:
Identifier X
→ Product B
Now the marketplace may face a product-data conflict.
Depending on its policies and systems, this could contribute to:
- Incorrect product matching
- Catalogue conflicts
- Listing errors
- Wrong product information
- Customer confusion
- Fulfilment problems
GS1 notes that many marketplaces use the GS1 database to verify whether a GTIN is linked to the relevant company and product.
🔍 Problem 5: Product Verification Becomes Difficult
Verification works best when an identifier points clearly to a known product record.
The basic relationship should be:
Unique Identifier
⬇️
One Defined Product
⬇️
Product Record
⬇️
Verification
If the identifier points to multiple unrelated products:
Identifier
⬇️
❓ Product A?
❓ Product B?
the verification process becomes ambiguous.
📋 Problem 6: Product Databases Can Become Inconsistent
A product database might contain:
| Identifier | Product | Brand | Size |
|---|---|---|---|
| 1234567890123 | Mango Juice | ABC | 500 ml |
| 1234567890123 | Apple Juice | XYZ | 1 L |
The identifier column is no longer uniquely identifying the product.
This can create problems for:
- Search
- Reporting
- Analytics
- APIs
- Inventory systems
- Product pages
- Marketplace feeds
- Verification services
A properly designed identification system should therefore maintain clear relationships between identifiers and product records.
🔄 What About Product Changes?
Another common question is:
“If I slightly change my product, can I continue using the same identifier?”
The answer depends on the identification standard and the nature of the change.
Within the GS1 system, certain product changes require a new GTIN, particularly when the change affects the consumer, legal requirements or supply-chain handling.
Example
Suppose a company sells:
Shampoo — 200 ml
and later introduces:
Shampoo — 500 ml
These are different product variants and generally require separate GTINs under GS1 rules.
The purpose is simple:
Different product → Different identity
🧩 Product Identifier vs Individual Physical Unit
There is another important concept.
A product identifier such as a GTIN generally identifies a product class/trade item, not every individual physical unit.
For example:
GTIN
= identifies the defined product
while:
GTIN + Serial Number
= can identify an individual instance of that product.
GS1’s traceability documentation distinguishes class-level GTIN identification from instance-level identification using a GTIN plus serial number.
🔐 Why Serial Numbers Can Be Important
Imagine a company manufactures:
10,000 identical smartphones
All smartphones may have the same product identifier for the product model/variant.
But each physical phone can additionally have a unique serial number.
For example:
GTIN: 1234567890123
Serial: SN000001
Another:
GTIN: 1234567890123
Serial: SN000002
Together:
GTIN + Serial Number
can identify an individual physical unit.
This provides greater granularity for applications such as traceability and asset-level identification.
🌐 How 91iD™ Approaches Product Identity
91iD™ is designed as an independent/private product identification and verification network.
Its architecture creates a structured relationship between:
Company
⬇️
Product
⬇️
Identifier
⬇️
Verification Record
The 91iD™ identifier format is:
91 + 7-digit Company ID + 3-digit Product ID + 1 Check Digit
For example:
91 | 1234567 | 001 | X
Here:
- 91 = 91iD™ system prefix
- 1234567 = Company ID
- 001 = Product ID
- X = check digit
The system is designed so that product identities are allocated within the company’s product range rather than allowing the same core identifier to be freely reused for unrelated products.
🔒 Why Non-Reuse Matters
Suppose Company ID is:
1234567
and Product ID:
001
That product receives a specific 91iD™ identity.
If the company later registers another product, it should receive another product ID rather than taking the old identity and assigning it to a completely different product.
This creates a cleaner historical record.
Conceptually:
Product A → Identifier A
Product B → Identifier B
Product C → Identifier C
instead of:
Product A → Identifier X
later
Product B → Identifier X
That distinction is fundamental to reliable product identification.
🧠 Why Historical Identity Matters
Imagine that a product identifier was used for Product A for five years.
During those five years, the identifier appeared in:
- Product catalogues
- Invoices
- Websites
- Marketplace listings
- Customer records
- Inventory systems
- Marketing material
If that identifier were later assigned to Product B, historical records could become confusing.
Someone looking at an old record might assume the identifier still refers to Product B.
This is why identifier management needs clear allocation and lifecycle rules.
🔍 What Happens When a Duplicate Is Detected?
A good identification system should not silently create two unrelated product records under the same unique identifier.
Instead, the system should be able to identify the conflict.
For example:
⚠️ Identifier Conflict Detected
Identifier: 1234567890123
Record A: Product A
Record B: Product B
Status: Requires review
This type of control can help prevent incorrect product information from spreading through downstream systems.
🚨 Duplicate Identifier vs Duplicate Product
These are two different situations.
Situation 1 — Same Product, Same Identifier
Product A
→ Identifier X
Product A
→ Identifier X
✅ Usually normal when multiple physical units are the same defined product.
Situation 2 — Different Products, Same Identifier
Product A
→ Identifier X
Product B
→ Identifier X
⚠️ Identifier conflict.
Situation 3 — Same Product, Different Unrelated Identifiers
Product A
→ Identifier X
Product A
→ Identifier Y
This can also create confusion if both identifiers are being treated as the primary identity of the same product without a defined relationship.
GS1 states that each product needs its own unique GTIN and, within its system, a product should have one GTIN.
🏗️ Why Unique Identifiers Matter for the Future of Commerce
Modern commerce depends on information moving between many systems.
A product may move through:
Manufacturer
⬇️
Distributor
⬇️
Warehouse
⬇️
Marketplace
⬇️
Retailer
⬇️
Customer
At every stage, the identifier can act as a common reference.
If that reference is ambiguous, information can become difficult to synchronize.
If the reference is unique and reliable, systems can connect their records more effectively.
🌍 Unique Does Not Mean “Only One Barcode Exists”
This is perhaps the most important concept in the entire article.
A unique product identifier can appear on millions of identical products.
For example:
1 Product Definition
⬇️
1 Identifier
⬇️
1,000,000 Identical Physical Units
This is perfectly possible.
The identifier is unique to the defined product, not necessarily to every physical copy.
For individual-unit tracking, additional serialisation can be used.
GS1 distinguishes GTIN-level product identification from GTIN + serial-number identification of individual instances.
⚠️ Is Every Duplicate Number Automatically a Problem?
No.
This is another important distinction.
A number can appear in many different systems or contexts without creating a problem.
The real question is:
Is the same identifier being used to represent two different products within the same identification system or context where it is required to be unique?
If yes, there can be a genuine identifier conflict.
📊 The Simple Rule
A reliable product identification system follows a simple principle:
One Product Identity → One Defined Product
while:
One Product Identity → Multiple Identical Units
can be completely valid when the identifier is intended to identify the product class.
For instance-level identification:
Product Identity + Unique Serial Number → One Physical Unit
This distinction makes product databases much easier to manage.
🧾 Final Takeaway
When two different products use the same identifier in a system where the identifier is supposed to be unique, the identifier loses its ability to clearly distinguish those products.
That can lead to:
⚠️ Product confusion
💰 Pricing errors
📦 Inventory problems
🚚 Fulfilment mistakes
🛒 E-commerce catalogue conflicts
🔍 Verification difficulties
📊 Incorrect product data
A strong product identification system therefore needs more than just numbers printed on a package.
It needs:
🆔 Unique Identity
📋 Structured Product Record
🔍 Verification
🔒 Controlled Allocation
♻️ Clear Lifecycle Rules
This is one of the fundamental ideas behind 91iD™.
91iD™ is an independent/private product identification and verification system, not a GS1 GTIN system. Its purpose is to provide a structured digital identity for registered companies and products, with controlled company and product identifiers.
In simple words:
Different products should be distinguishable by their identifiers.
That is what makes a product identity useful.
❓ Frequently Asked Questions
1. Can two products have the same barcode?
If they are the same defined product, the same product identifier can legitimately appear on many physical units. If they are different products that require separate identities, using the same identifier creates a conflict.
2. Can the same GTIN be reused for another product?
No. GS1 states that a GS1 GTIN cannot be reused for another product once assigned.
3. Does every physical product need a different GTIN?
Not necessarily. Identical units of the same defined product can share the same GTIN. A GTIN identifies the product/trade-item definition; a GTIN plus serial number can identify an individual physical instance.
4. What happens if two different products have the same identifier?
The identifier becomes ambiguous and can cause problems with product lookup, inventory, pricing, e-commerce catalogues, fulfilment and verification.
5. Why does every product variation need its own identifier?
Different variations such as size or colour may need separate identifiers so that retailers, marketplaces and supply-chain systems can distinguish what product is being sold or ordered.
6. What is the difference between GTIN and serial number?
A GTIN identifies a defined product/trade item. A serial number can distinguish an individual physical instance when used together with the GTIN.
7. Does 91iD™ use the GS1 GTIN system?
No. 91iD™ is an independent/private product identification and verification network. Its identifiers are not GS1 GTINs.
8. Why is identifier non-reuse important?
Controlled allocation and non-reuse help preserve the historical relationship between an identifier and the product record it represents.
🌐 Explore 91iD™
91iD™ — Independent Product Identification & Verification Network
Identify. Verify. Connect.
