Against what most of us start out learning as good darkroom procedure--for consistent results use fresh chemistry--every once in a while I see references to aging chemistry.

Gordon Hutchings, for instance, in _The Book of Pyro_ writes that the A (pyro) solution in PMK benefits from age, and that he keeps a large jug of solution A in a constant stage of aging, and he back-blends some of the vintage pyro with each new batch of pyro.

Users of Harvey's 777 developer seem to have a very firm belief that the first batch of film is never as good as subsequent batches, kind of like the first crepe.

I think this is also said of some color chemistry in commercial processing, that the replenished chemistry provides better results than the original batch.

On the other hand, D-76 and ID-11 are known to give contrastier results with age, and most common developers just go bad as they oxidize.

Any theories, hypotheses, or views on what can be going on here? Anyone out there (intentionally) aging their chemistry, or have a good sense for why some kinds of chemistry might benefit from age?