Unfortunately they are more than that, perfectly good and sealed though which is the annoying part.
Can the carts be re-chipped ?
Ive seen somewhere (not on these forums) that you can obtain replacement chips – are you aware of that ?
Yes, you most definitely can, but just bare in mind that they are dated for good reason. I’d imagine Mimaki are a little over cautious with their dates but if you’re talking years out of date I’d be very wary. Particularly if you have a contract on the machine, it will likely invalidate the printhead.