An interesting aside Ilford's sub-contractors now use Dimezone and I've only seen people complain about the shelf life since that change. I make up my own chemistry in bulk, I re-jig the formulae to allow similar concentration to comercial offerings. Because I was spending most of the year abroad and only 2 visits a year back home and a darkroom I've pushed sorage far more than in the past. A PQ developer in a part filled 5 litre bottle will last me over 2 years.