I think the issue of "a long time" is highly subjective. While your most recent experience is nearly a year ago (and, in the grand scheme of things is not a long time), the Cast Member you spoke to deals with priority seatings on a daily basis, and in his frame of reference, 4 months may be a long time.
In any event, that is quite a moot point, as things are always changing at WDW and the past and the present are two distinct realms no matter where you happen to be.
I don't know the reason, I would assume that there is a special event taking place at the Crystal Palace that evening, or that their policy is now to only take walk-ins after a certain time (which may make more sense. A PS only guarantees the next available seating, not an immediate seating, and the dinner buffet is quite popular).