My TMY negatives developed in 777 have been noticeably thin of late, even with extended development. N+1 for 19 minutes at 72 degrees prints on grade 3 Azo with great difficulty.
Bottom Line: somewhere in the 6-9 months range it depletes, no matter how much you replenish. At least I think so. I'll order another 4 gallons tonight. After I mix up a fresh couple of gallons and try it out we'll know for sure. Until fresh 777 arrives I'm using Pyrocat.