There’s a serial number on each cartridge that is reported to the printer. If the printer doesn’t see the serial number, it thinks is a new cartridge.
The method I seen work on the 7950 is to tape over the contact pins on the catridge that handle the serial number. Insert the cartridge, remove it, take off tape, and reinsert the cartridge.
HP did this as a way to prevent the cheap ink refill business from reusing their cartridges. After all the ink is HP’s bread and butter and why it cost so much. (They sell the printers at a loss hoping to make it up in ink cartridge prices)
The ink refill kit places will tell you how to bypass the check with exact directions for each printer.
I, too, get perfect results printing on plain paper with my Epson NX300 - probably because the paper absorbs the ink as it hits the paper and dries. My problem occurs when I print on Testors decal “paper” - which is really not paper, but a surface to hold the printed pattern until I spray it with the bonding solution. As [the ink] is drying and shrinking, cracks form in it because the slick surface can’t hold it in the same spot. And this happens before I spray the sealer on it.
Water never touches my decals until after I have sprayed them with sealer, and they hold together fine when I soak them to apply them - except for the cracks as I mentioned earlier.