As many here have said, I wouldn't pay full price for them, but I would use them without concern. I'm not sure how expired is safe, but I've routinely had inks in my printer up to a year or more past the expiration date (I haven't installed them that far out, but I've certainly used them...) The most important exception is HPs (and any other printer that detects ink age with a chip and complains - I don't know of anyone else doing that in large format, but many smaller printers do - I don't think all the offenders are HP products). I would also be wary of old aftermarket ink - it may or may not have the same settling characteristics of OEM ink.
In fact, I personally wouldn't use aftermarket ink in a large-format printer at all. The printers are much more expensive than a consumer printer, and the ink is much less expensive per ml, so the savings are less and the risk is greater. How much to risk is a personal decision - I'd absolutely try it in a $69 printer with $70 refills (they exist), and third-party ink isn't getting anywhere near my Pro-2000 - I'd have to think about it in between. Unfortunately, cheap printers are the most heavily chipped!