From the Auto Care PIES 6.7 documentation rev.4 p.77 & PIES 7.1 documentation p.110

GTIN Summary
From a data perspective, we treat a  GTIN data format as always 14 digits, regardless of whether a GTIN  is a GTIN-13,-12, UPC or, GTIN 8 – the GTIN ‘Block’ of 14 characters is filled with leading zeros (Regardless of what we do with the Barcode).  The Barcode itself is likely a GTIN-13 (EAN) or GTIN-12 (UPC).  Small packaging can attract the GTIN 8 (likely such things as bubble gum, cigarettes, etc.)  These three formats of barcodes are all read at the Point of Sale system. 
There are other barcodes, however, which are read throughout the logistics chain.  These are represented as GTIN-14, and tell the warehouse and shipper different things: 
GTIN-14 supports Pack-Levels.  In the GTIN-14 data format, Package Levels are read from the leftmost number.  Package Levels can be a number between 0 and 9;  a ‘0’ indicates the GTIN represents a single unit.  A ‘9’ represents a unit where the weight, measure, or volume sold can be variable.  Package Levels 1 through 8 are defined by the company using them.  There are no standard definitions to follow. 
There are some practices that companies are adopting, for example: 
Pack Level ‘0’ – Each (Consumer Selling Level) 
Pack Level ‘1’ – Inner Pack (Non-Shippable) 
Pack Level ‘3’ – Inner Pack (Shippable) 
Pack Level ‘5’ – Case  
Pack Level ‘7’ – Pallet 
These would properly correspond with the AAIA Pack Level Tables used in the Package Segment. 
From a DATA perspective, a GTIN will always be represented as a 14-digit number, regardless of its use. 
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