FWIW, in the datasheet, Kodak lists the following as the capacity for a replenished system. I read this is as "discard and start over" when you hit these amounts(2017 datasheet J78, from when D76R was still available, here
https://business.kodakmoments.com/sites/default/files/wysiwyg/pro/chemistry/j78.pdf ). If you read a bit more into the details, they give 9600 sq. in. of developed film as the basis for these numbers. I also think of this in terms of a single sheet of 8x10, or 80in
2 being a "standard unit" of film(my made up term, but hopefully makes sense given how it's referenced in a lot of processing documentation), and 1x 120, 1x 135-36, and 4x 4x5 are all equivalent to that number(back of the envelope math says 2 sheets of 5x7 will come a bit short of this-if you want to be exact 7 sheets of 8x10 have the same area as 16 sheets of 5x7, or that 274 sheets of 5x7 would be the aproximate capacity)
FWIW, I shoot at a volume where I'd probably come out financially ahead by replenishing, especially if mixing all from scratch, but bear in mind that they also recommend discarding and starting over after 4 weeks. Sometimes I use 2-3 gallons of D76 in a month, and sometimes I'm butting up against the the shelf life of a stock solution even using it 1 shot(although I've DEFINITELY stretched Kodak's recommendation for 2 months for a partial bottle, and in a pinch have used a partial bottle mixed 8 months or so before, but wouldn't have done that if I weren't developing purely for camera and lens function testing).
They also offer these instructions for TMAX film if you want to develop it in a replenished system. Note that this is stated as having a 1 month life before the whole volume should be discarded.
There's also these instructions for replenishment volumes to use for both TMAX and standard film
(the first paragraph refers to TMAX replenishment-it was cut immediately after the above text to avoiding having too long of a screen shot).
There's no discussion of replenishing mixed TMAX and conventional films. If doing so, I'd think the "safe" option(aside from segregating developers for the respective film types) would be following the TMAX regime for all solutions. I'd also go out on a limb and suggest that Delta films would be recommended to follow the same routine as Kodak, although as I understand it there are some technical differences that make Delta films a bit of their own beast(but seemingly a bit lower maintenance/more tame than TMAX) for this.
Speaking purely for myself, my main motivation for looking at replenishment is that I've been shooting a decent bit of 70mm long roll recently, where I'm often processing the equivalent of 3-6 rolls of 120 in one go(and really a bit more even for an equivalent length since it's ~9mm wider, although cameras also still shoot the same image area and there's often less rebate information than on 120 film). The long roll tank I use takes 1.6L of solution, so there's definitely some motivation for stretching developer as far as I realistically can while still keeping reasonable results). I don't think anyone has made a tabular grain film in 70mm, so at least that's not a consideration.
