Epson K3 limited lifespan in printer?
Espon says 6 months after opening.
But the experience of many is that is a very conservative number.
I've had matte black ink for my R2400 that has been good for 3 years. I usually use the photo black and rarely the matte black. So it can take a very long time for me to use up a matte black cartridge.
A few of the less used colors in my Epson 7900 have taken over a year to use up. Again, with no apparent problems or loss of color quality.