......... but it is my understanding that with DDX it's keeping properties are adversely affected by having it at working strength.........
This is the case with every developer, is it not?
For what it may be worth, this is cut from an Agfa pdf for Rodinal Special (a.k.a. Studional) which is a developer something like DD-X (nothing like normal Rodinal):
"The concentrate will keep for at least two years in the original
pack. Developer mixed ready for use will keep for three months
in brimful tightly capped bottles. Used developer should be
stored separately from fresh."
And from the same document, on the subject of reusing this made up developer:
"Lengthening time for multiple batches
(small tank, tray, drum)
To ensure consistent speed yield and contrast, the developing
times for each successive batch must be lengthened. It is not
possible to give exact times, since these are governed by the
idle time between two batches and the method of storing the
developer (glass or plastic bottles, brimful or part-full, capped
bottle). If used developer is kept in brimful tightly capped
bottles between batches, the guiding figures given in the table
below should be used.
The following is a guide: after processing one film in 500 ml
developer, lengthen the developing time by about 10 %. With a
five-litre tank volume lengthen the time after ten films.
Idle time between ________Development lengthened
two batches ____________by
few hours (but develpment ________none
on same day)
1 - 3 days _____________+ 5 %
4 - 8 days ______________+ 10 %
1 - 2 weeks ______________+ 15 %
over 2 weeks ______________+ 20 %
<end of quote>
edit: sorry about the formatting, but I think you get the idea