This is a complex issue because we have no standards, it's bad practice to keep reusing and storing working strength paper developers which is why all companies don't recommend it. Having said that though I know people who use PQ developers in Nova slot processors and replenish and they last weeks dilute.
Originally Posted by zsas
One issue is print quality with any developers stored partially used and there's to many variables, there would almost certainly be shifts in tones with warm tone papers and then some papers have a degree of developer incorporation so are least affected by developer degeneration.
It's about 50 years since I made my first prints and in all those years I've never needed to store part used mixed print developer. I've used PQ developers for over 40 years without an issue and yes stored for over 2 years.