Yep, this is the best I could find when searching on "ilford multigrade developer longevity":

The links are to two PDFs, which give some info about the shelf life of the chemicals. In
summary, it says:

"Diluted MULTIGRADE developer will stay in good condition in an open
tray for two working days, at dilution 1+9 and for one working day, at
dilution 1+14. Unopened bottles of MULTIGRADE developer will keep
approximately 24 months. Tightly capped half-full bottles will keep for
up to 6 months."

The links are:
https://www.emsdiasum.com/docs/techn...rchemicals.pdf
and
https://www.reddit.com/r/Darkroom/co...king_solution/