I have a Nova processor in which I use Kodak RA4 colour developer. I made the working solution perhaps 6-8 months ago, (I didn't keep a check.) It has been used fairly intensively and replenished when needed up until about 3 months ago.After that did not use it because I had no reason to do colour printing. The lids were all replaced and then the top of the processor was covered with clingfilm whilst it was still warm. As it cooled down it caused a semi vacuum inside.
I have just kickstarted the processor today and the very first print out of the developer was as near as dammit, spot on, colour wise. Saturation was up to scratch as well
Just how good is that for longevity of developing solutions? Truely amazed!