Digital BW, The Print

Hi,
I have an Epson 280 with the Paul Roark recommended MIS inks (4 oz bottles).
There is now very little difference between groups of inks.
[Black] {Cyan, Magenta}  {Yellow, Light Cyan, Light Magenta].

Do these inks have a shelf life? I have had the ink for over a year.

Thanks

Mike Johnston