Brian-
You can check in the printer utility's paper list to see what the date is for each paper calibration. My guess is that the calibrations are not being tossed out, but that for some reason the printer is saying that new ones are due. My well used Z3100ps asks for calibration more recently than it used to, and will sometimes tell me I need a new one after only a week or two. The documentation from HP says that environmental changes (not really an issue for me here in Hawaii) and other factors, in addition to time are taken into account in asking for calibration updates. Unfortunately, they really don't give the criteria for asking for fresh ones. In my experience, it seems to make little or no difference if I recalibrate every time it is asked for if I have a recent one already in the system. FYI: opening the printhead compartment always triggers a new request, even if you don't remove the heads.
