Why No TPG?

It's largely a self-imposed exile - the big American TPGs have generally recognised their own lack of experience in identifying, authenticating and grading ancients. PCGS has never graded ancients; neither has ANACS. NGC until recently only graded ancients with reluctance. Old ICG did Roman but not Greek.

There is a specialist ancient coin " TPG" - ACCS, run by David Sear, the guy who compiles the ancient Greek and Roman catalogues. They authenticate and grade, but don't slab.

Which leads us to the other major consideration. Ancients collectors just don't like slabs. There's no collector demand for them.

@ian I'm not sure that's a fair comparison, since these coins have been buried for 1500 years. Granted, I don't know if that's more or less likely to damage a coin than being exposed to handling, but I think it's fair to say that it's different.

I came across this the other day:

http://www.ngccoin.com/ancients/index.aspx

Which says (at the very end) "Authenticity and attribution represent the opinion of NGC Ancients and are not guaranteed, nor is any guarantee implied."

IMO this reduces the value of the TPG. Sure, it's nice to know that it's genuine in their opinion, but it would mean a lot more if they stood behind that opinion.