"Dan Luke" wrote
One finds many 20+ year old aircraft advertised with engine time =
airframe time, both in the neighborhood of 1000-1600 hours. Now, it is
my undersatanding that aircraft engines have a calendar TBO as well as a
tach TBO.

Your understanding is correct.

however, prices for these aircraft do not seem to reflect
engines that are beyond TBO.

That's simply because lots of people are either not aware of this or
don't care. Most owner-flown engines hit calendar TBO long before
hitting tach TBO. On the other hand, most owner-flown engines also
need significant engine work well short of TBO. Coincidence? I think
not.

Is calendar TBO something that is generally ignored?

Yes, but so is tach time. As long as the engine keeps making power
and the compressions are good, it will be run.

Should a prospective buyer make a hard negotiating point about it?

Won't work. Enough people don't know or don't care about the problem,
so a seller would have to be an idiot to back down.

Michael