I would not vouch for this being the official response, but here is what I have done with RA-RT to get over 4 years out of the RA-RT 4x10L.

Transfer the developing agent containing concentrate into filled full small glass bottles. Read the storage guidelines. If it saye store something like 5-40C, well, make sure that the little bottles are as close to the lower end as you can. My fridge has in the past kept one bottle, but it did not seen any more or less active as an unfridged one that lived in my 18C basement after 3 years.

Mix up just what you need. I worked out the proportions and just mix 2L at a time.

For e-6 I have bits of the old 'makes 10L' kits from Kodak. Here the isolate the CD agent of the second developer into full glass has shown to work. One only 3/4 full after 4 years is a black tar; the other full bottles are the light amber they went in as, and still work fine.

I have yet to buy commerical C-41 from Kodak, but the same strategy should extend whatever the rated life is.