What is the difference between AI (01) and AI (02)?

The Application identifiers (AIs) (01) and (02) are used to store product identification numbers i.e. GTINs.

Application Identifier (01)

• The AI (01) is used to encode the GTIN (barcode number) of the actual item being labelled e.g. an outer case.
• (01) is used where the outer case (logistics unit) has its own unique GTIN.
• This GTIN is distinct from the GTIN of the product contained inside it.

Application Identifier (02) + (37)

• The AI (02) is used to store the GTIN (barcode number) of the item contained within the box or pallet 
• This is often used for single items that may not have a corresponding case code or;
• At pallet level to declare the GTIN of the outer cases stacked on the pallet
• AI (02) MUST always be used in conjunction with AI (37) which declares the number or quantity of the items

Further information on Application Identifiers can be found here.