Wow. Thanks for all the info. That's really going to help me in future purchases as well as help date items that I already own.
So, for the purposes of illustration, here are a few examples:

Mike Tomczak Bears. "B-Z" = 1989/December


Jim McMahon Bears retail authentic. "E-S" = 1992/May


Neal Anderson Bears. "EU" = 1992/July "2" = ?


Mike Tomczak Bears. "A-O" = 1988/January


Other than the "2" on the Anderson jersey tag, everything seems to make sense. Thanks again for sharing this valuable information.