I see iSign is skeptical.
We reset the date on ours, less than a month after we bought it, more than 2 years ago.
We have not had any problems relating to the date on the inks, and have used inks that were a year or more out of date, but sealed at the time of install.
Our supplier only have had inks that were nearly expired or expired anyway, and it would be very expensive to keep only inks within date. Would have to throw away most cartridges half full. I helped a fellow nearby Mimakiowner a year ago or so too, we shared the suppliers stock of expired ink, got 20 cartridges at half price... That's more than $25 saved... More like $1500 saved... And ink was just as good as the "new" ones.
You can set the date at whatever you feel comfortable with after resetting the battery, no other important setting get wiped out. You can for example set the date at 6 months ago, which will keep them working 6 months extra. Ours was set 4 years earlier, as the inks don't last longer than a few months in the printer anyway, the expiration date is crap, and is only there to allow Mimaki to sell more ink.
I know I will get negative reactions to this, but it would be interesting to see if anyone have gotten problems from this reset or from using chips without expiry date, not just the scepticals that have not tried for themselves...