>> I never said that the accusative and genitive were actually
> I never said you did. I said you posit a preform *-om for both,
Doesn't matter. You're wrong on all counts.
In my view, the preform of the accusative is simply *-m right back
to ProtoSteppe since it is reflected identically in Uralic. The
source of the genitive plural is something different altogether
which I suspect derives from *-ána, shortening to postSyncope eLIE
*-án which then becomes *-ám sometime in the Late IE period due to
analogy with accusative *-m. This yields *-óm after Vowel Shift.
Originally the genitive plural would have been a locative (something
I just said before and many times before that) but you didn't listen
because if you did, you'd realize that this means automatically that
I _don't_ posit the above.
> although the genitive plural has a long vowel in all languages that
> can show the difference between *-om and *-o:m.
In athematic declension, the accusative is *-m and the genitive
plural is *-om. The thematic then is simply the product of thematic
vowel plus the athematic endings. If you do the math, merely
grafting the same endings *-m and *-om to thematic stems would
otherwise produce a homophonous *-o-m.
If homophony weren't a threat to thematic declension during a preIE
stage, we wouldn't even be talking about *-s-yo, the clearcut byproduct
of the inevitable homophonies between the expected thematic nominative
singular *-o-s < *-o- + *-s, nominative plural *-o-s < *-o- + *-es
and genitive plural *-o-s < *-o- + *-os!
As for the genitive plural, there was only a possible TWO-way merger
which supported a more trivial solution of *-o-?om rather than the
singular's more creative solution with *-yo.