For me obsolete means that it is not the current chip being ordered for their racks/tables. They still may be on the table and still cashable at the cage, but not the ones currently distributed. This is a more open definition that others.

LE's and COMMs by their nature are (often) made one for one run and cannot be obsolete.

Chips from closed casinos (other than LE's/Comms) are automagically obsolete.