HP Plotter Ink

This is probably a bit off-topic, but as it specifically deals with using out-of-date supplies, I'm hoping no one will object and that people here might have some ideas. I've recently inherited a couple of plotter rooms with HP 1055CM and 5500PS plotters. These are the 36" to 42" variety, and the Ink cartridges and Plotter Head/Cleaner packs tend to each cost as much as a home Inkjet printer. I spot checked the supplies earlier this week and discovered that with very few exceptions most of it is out of date, with dates ranging from 2002 through 2006. Does anyone have any idea how safe it is to use old Ink or printhead/cleaner kits? How about any guidelines for when the stuff is to old. Obviously this is not the sort of question I can get a good answer Unlike the home inkjets these do not seem to have any time-bombs built into them where they stop working after the date is passed. Thanks, Zane