Audi/VW Steuergerät Vergleich: Find the Best!

Since I suspect my control unit is broken, I have a question:
My engine control unit (ECU) has the part number 028 906 021 F. I might be able to get one to test and potentially keep, but it has the part number 028 906 021 B. What are the differences between these two ECUs?
Both are from the 1Z engine, but mine is from an Audi B5, and the one with "B" at the end is from a 1994 Passat 1Z. Mine is from the year 1995.
Are they the same, or what is the difference between them?
Is the difference significant enough that the other control unit wouldn't work?
Thank you and best regards.
Thilo.

EDIT: Which letters might still be usable at the end?