After you file

Huh?  Don't get confused here. 

The use of the term "12a" is just a way to indicate the first line of box 12.

My W-2 forms had multiple boxes, actually labeled 12a, 12b, 12c, 12d,   but mine only used box 12a with a code D after it, and a $$ amount......since I only have $$ sent to a 401k, and the other 12b,c,d boxes empty.

Like, a person could easily have had three lines in box 12 with the following....IN ANY ORDER:

Box    Code    Amount         (my note as to what for)

12a     D           3000                (401k Contrib)

12b    AA          2000               (Roth 401k Contrib)

12c     W          4000                 (HSA $$ )

12d

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So the HSA contribution could be in any of those boxes, depending on how many contributions need to be noted.

One could say they have a box 12 with a code W and a $$ amount

........or just say they have a box 12a with a code W and a $$ amount

.....essentially.....same thing...so don't get hung up on the 12a, 12b, 12c.

The only problem a few folks have, is seeing the box labeled 12a, and thinking the "code' is an A.

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Now, in the TTX software, TTX doesn't bother labelling the multiple boxes as 12a, 12b, etc.....just lets you enter as many separate lines for box 12 as you need for any codes and $$ you actually have on your W-2