Okay, ready for a surprise?
I bought some Epson carts. I put in the Light Black first, as this was the cart that started off the problem. And guess what - not only did it fix that cart's "not recognized" message on my printer, but it also fixed the message on the matte black one! So I tried putting back the Light Black from InjketMall to see if the problem would return, and it did, but not only for that cart, also for the other Matte Black one that was giving me trouble.
How can one cart being pulled out and re inserted affect another cart being recognized?
In any case, this seems to indicate that the fault is not with the printer. I tried all the new chips recently ordered for those two carts without any success before the last resort of trying some Epson ones.
NB: I saw your last reply after writing this and am not sure how it squares with the results I've just described. To my knowledge I've never updated my printer's software, unless it does it without notification.
Anyway of checking my software for updates and then rolling them back? I've not knowingly done any.