Couple weeks ago I used Xtol that I had mixed november 9 2007 and bottled into large 40oz beer bottles
kept in basement on the concrete at about 43-50 degrees

Well, the bottle I used was half full and has been used on/off since being mixed

Worked fine. Negs were done at 9 minutes. I just guessed 9. assorted 35mm film had been shot years earlier so "overdeveloped" it
3 rolls large paterson tank

Mix it with distilled water
dont whip in air while mixing maybe
I use wooden forks
keep moderately cold
seal with saran wrap and screw caps

I've never had failure.