There is a very good reason that ink carts have expiration dates. And all you "experts" out there that say it's alright to ignore expiration dates should be aware of ink chemistry and physics before you give such "anecdotal" advise.
First of all, pigments do settle, as some have pointed out. Just shaking the cart can help in this regard, but not totally. There can also be a coagulation of pigment particles. Shaking will not break this up. With enough of these coagulates, your Epson dampers will get clogged and lead to ink starvation problems.
No easy fix for this coagulation problem short of sending the ink back through a grinding process. Much cheaper just to buy new ink.
The modern solvents and co-solvents do a remarkable job of keeping our inks free flowing in our printers. But we should not buy ink in quantities larger than we can't use up within 6 months to a year. And if you go out on a limb and buy expired ink-- you better use it up PDQ and keep your fingers crossed.
The problem most "hobbiest" printers have is they don't use their printers enough. The more you use them, the better off you are.
I'm not affiliated with any vendor or manufacture, and I've warned all of you in the past about the foibles of false economy in using old inks. I can't emphasize enough to use fresh ink, if you want your printer to keep working. Personally, I've had incredible experiences with my 5-year old HP Z3100. Very rarely do I ever Perform nozzle checks, or head cleanings. It just seems to be ready to print when ever I send it files. And I hear similar reports from Canon owners. :-)