That's part of the P800 scheme. I saw this over a year ago, when the ARCs stopped resetting and the behavior of testing ARCs showed. It will accept a lower ink value but it will not accept an increased value once it has seen the last reading and serial.From the weasel word in the patent they write the decreasing ink estimate to the eeprom, among other data. This is needed if cart is removed and replaced in the same or another machine. But the memory will not accept an increasing value-acts like a ratchet-or screw.
Can't find any Canon patents but these guys constantly cross license.