Some HP printers (OZ) do write mono or color counters to ROM after every page, it it keept it in RAM.

The printers has to print 10 pages or more before mono or color counters are written to ROM.

If you power up the printer in the morning and print 8 pages during the day and power off the printer then the mono or color counters is not updated.

The Total counter is always written to ROM and you will then see that the Total counter is larger than the Mono + color counters.