The numbers in J78 for straight, one-shot D76 are indeed 4/litre.
Personally, I like using a replenishment routine.
What a strange thread. Surely the pedantics of developer usage, diluted or otherwise are of no importance when processing what you shot into a printable negative?
In practice it's actually extremely important to have your processing under your full control to get good consistent results.
In the late 1960's I used the technique of increasing dev times in unreplenished developer, I soon switched to replenishment as it made sense and results where totally predictable.
There's various development options but which ever is chosen it's important to learn to get it right that way you can concentrate on making images with confidence.
Or use the DD method....dilute and discard....works for me!
It seems counter-intuitive to me to re-use a single batch of Xtol until it runs out of oomph.
If you stopped after a few films,depending on your developer volume,you will have a "seasoned"batch of developer,which you can keep at a stable level of activity by replenishment.
Xtol,being its own replenisher,makes it more amenable to this than D76.
I first learnt about this on this forum - I'll never go back.