"Theoretically then, would their be any such thing as an obsolete AC chip?"

In MY opinion, YES! Anytime a chip is no longer in use, or is un-obtainable from the casino in Atlantic City.... it is obsolete. That's just MY definition for A.C. chips. Could someone bring back a stack of otherwise unobtainable LE's and present them for redemption at the cage... Yes, but they could also present first issue H&C Resorts chips to the cage also for redemption. Brighton chips are still redeemable at Sands. Boardwalk Regency chips are still redeemable at Caesars. Golden Nugget chips are still redeemable at Hilton. Original Hilton chips with the rainbow are still redeemable at Trump Marina. I don't quite understand the logic of those who say "if they are still redeemable they are not obsolete" or if a redemption period has passed.

One must separate Las Vegas regulations from Atlantic City regarding this question.