Just FYI, we checked in for a pair of business class flights from PHL airport on Xmas day - one, departing in just less than three hours, and the other departing in almost five hours) and there was no problem at all with the early drop-off of the checked bags for the later flight.
The AA webpage still exists which does NOT mention explicitly how early bags can be dropped off in general, but which DOES still explicitly list only those airports with a shorter (I think it's four hours) earliest bag drop (and, PHL is NOT on the not-earlier-than webpage).
AA could make the information a little more clear, (I called in to AA in advance to ask about it, and it took AA's own staff a while to figure it out), but anyway the information presented in this thread seems to remain accurate.