NthreadsP problem

I'm trying to use the NthreadsP program to generate gear trains for
oddball threads (like 24.57 tpi) for my 6" a/C lathe. The problem seems
to be that the A/C gear train starts out with either a 16 tooth or 32
tooth gear 'on the spindle' but the NthreadsP seems to assume you can
put any gear on the spindle you want.
I tried restricting the gear train to only those gears listed in the
Atlas book for 16 tpi (the leadscrew pitch) but it never gives me a
train starting with 32 teeth as the manual shows. What am I doing
wrong, or doesn't the NthreadsP work with the Atlas/Craftsman 6"?