I am not sure if this is interest to anyone but since there are thread about how long developer chemistry lasts, here's a data from my own experience.
I purchased a bottle of 1 liter Ilford Warm Tone paper developer and opened it on 6/27/2011. Used some of it a few times.
Then realizing I had a lot left, I decanted what's left into two 250ml bottles. That happened on 11/3/2011. That means the original bottle was left nearly half empty for about 4 momths+.
Those two bottle sat for a while, full, and capped. These were plastic bottles. I used one of them and when I got to it today, which is 01/17/2013, 1.5 year since the bottle was first opened, was half empty and the liquid was fairly brown but not pitch dark brown. It worked just fine. Deep black.... fast development.
The other bottle looks clear. Just a very faint sign of brown.
So.... it lasted 1.5 year minimum and perhaps much longer.
Just thought someone may be interested....