Making "significant" progress:

=A1&MID("thstndrdth",MIN(9,2*RIGHT(A1)*(MOD(A1-11,100)2)+1),2)

Yes, you did make significant progress... Nice going!

One of the problems with my coming into the Excel newsgroups armed basically
with only my knowledge of the compiled VB world is I tend to think in VB and
then translate that to either VBA or spreadsheet formulas. This means that,
when translating, I have to be aware of the differences between how
identically named functions perform. In this case, I completely forgot that
the spreadsheet version of the MOD function, unlike the VB/VBA Mod function,
never returns negative values. I needed to see your formula in order for me
to remember that fact. Had I remembered that back when I first translated my
VB Ordinal function into the spreadsheet formula I originally posted, I
would have abandoned the ABS function call (which was there solely to work
around the fact that VB's Mod function can return negative values) in favor
of the MOD(A1-11,100)2 logical expression you used (although I am sure it
would have taken me some "fooling around time" to arrive at it). Then,
progressing through the "formula shortening" process I posted earlier in
this thread, I would have ended up posting this final formula...

=A1&MID("thstndrdth",1+2*MIN(4,RIGHT(A1))*(MOD(A1-11,100)2),2)

As it turns out, it is the same length as your formula above! Now, I used my
originally posted formula as its basis, which accounts for the difference in
the construction of our two formulas; although interestingly, we used all
the same functions (in different ways, of course). However, I am glad that I
didn't come up with this formula yesterday because, more than likely, you
would not have ended up posting the formula that you eventually did. Aside
from the fun and satisfaction of your doing it yourself, I (as someone who
was a math major back in college) find our two different mathematical
constructions, which end up yielding the same result, a fascinating thing to
study.

Rick