I mixed everything fresh except the hypoclear, because the color still looked ok.
As for the Tmax, I mixed it per the instructions to the working solution, so there was no dilution involved as there would have been if I were using D-76. And I did use two concentrates--one had been in the cabinet for a while, and the other was new.
I wasn't sure about the stop, it was in the original container, and I used the original instructions. Maybe I should just make up a fresh batch with the orange concentrate to be sure.
So as far as the fixer and hypo-clear, I went ahead and disposed of them. But in the future, they are ok to save? As for the hypo-clear not being made in a while, I work in a community darkroom that hasn't been used over the summer. The hypoclear was still an ok color, so I didn't make any of it yesterday like I did the other chemicals.
Thanks for all your help! I've not had a lot of experience mixing chemicals on my own yet, so I'm still figuring some things out.