I kind of doubt you could play a chip that the dealer or pit boss didn't recognize, even if the Sands had issued it a long time ago. I'd call it obsolete. However, I never play in Atlantic City so if ArchieB says they will let you play (as opposed to redeem) any chip ever issued by the Sands, then that isn't an obsolete chip by my definition.

There are so many other properties of a chip, like can you buy it at the casino, can you cash it at the casino, can you cash it at ANOTHER casino, can you cash it at a Gaming Office.... that I think it helps to keep the Obsolete definition clean and simple. If it still serves its original gaming purpose, it's live; if not, it's obsolete. Note that that makes some 'obsolete' chips redeemable... but that's OK as that's another issue.