when you see a chip valued at less than face, it's a good sign that it is not redeemable. In fact, I would be surprised to find where that is not true (except perhaps in the case of an ncv chip). In Las Vegas, casinos are allowed to issue redemption notices, giving a final date to redeem those chips, after which, those chips are no longer redeemable. Happens all the time. I would guess that whenever you see a chip valued below face, the chip is no longer redeemable, otherwise, you could certainly get the face value for it (such is the case for virtually all chips in Atlantic City, even where the casinos are long closed).
Michael Siskin