TD-16 and TD-16R.

These products from `The Photographers Formulary` are claimed to behave like D-76 developer and D-76R replenisher, but with better consistency. Has anyone used these products and how are they different from what Kodak sell?

It`s probably better to ask the photographer formulary directly.

I believe there was an issue with storage PH levels (mixed working solution) with the Kodak formula that would give inconsistent results at different times in it's storage life.

I learned & standardized on Kodak D 76 and still use it extensively and haven't noticed any inconsistencies although I don't test PH before every session and read my negs with a densitometer.
I think Kodak claimed they rectified the issue anyway but Im not a chemist so I can't say.

I'd be interested in some of the more chemically astute members have to say about this issue if it exists.

While I don't recommend it, I had some working strength D76 in storage for over 12-13 months and it still worked.