hello,
in my very limited experience, any time ive seen such question, or asked it, most recently to Ilford about ID-11 etc. The answer always seems to be that as long as air tight etc etc that will last for long past the shelf life, you just will need to experiment with timings as will no doubt need a little longer to brew.
as i said though, i wouldnt trust a word i say, havent got a clue, me.