Supplemental Barcode Type Distinction

I'm kind of over my head here so please go easy on me if this doesn't make sense.

A customer is using EMDK and is examining the barcode type and says that there is no distinction between a symbology and the supplemental version of that symbology.  For instance, when the barcode that is decoded is a upc-e + 2 supplemental he says that there is no upc-e + 2 supplemental type, only upc-e. 

1. Is that true?

2. How is that distinction supposed to be made (data length perhaps?)?