I'm ready to buy the newly formulated black inks, both MK and PK, for my Epson 4900. I see in the directions that "You should not pour these new black inks into a cartridge that currently contains our regular black inks." and also that "These new black inks are fully compatible with both Epson and ConeColor Pro inks".
Is the part about not using the existing MK and PK cartridges on the level of "for best results", "strongly recommended" or "not under any circumstances"? I would rather not buy two new cartridges if I don't have to but I certainly don't want to cause any problems.