"What I like about TMX and TMY is that kodak instructions are to use the same development time so that sheets of both or rolls of both can be developed together. I am starting to think that this is wishful thinking."
Good Morning, Better Sense,
It's been years since I checked specific recommendations for TMX and TMY; since I normally use T-Max Developer, except for night shots when my dwindling stock of Technidol comes into play. The times I use for TMX and TMY are very close, but not exactly the same. I base my T-Max developing on the information which appeared in a magazine article test (which magazine?--dunno, it was probably 25 or 30 years ago); the recommendation was that TMY should get 9 minutes and TMX 10 minutes in a 1:7 solution. I use those times as "normal" and deviate from them depending on my perceived or recalled evaluation of a given subject's contrast level. For example, shots taken with direct flash on TMY, with slightly generous exposure, would probably get 8 minutes or 8¼ minutes development time, because of the relative harshness of the light.
I agree that, for non-critical work, both films could be processed together, say for 9½ minutes with at least acceptable results for each. If I were using roll film in that situation, I might also put the TMX on the bottom, the TMY on top, and pull out the TMY roll(s) with lights off a minute or so prior to the end time for TMX. The TMY would just get an early start in the film washer while the TMX went to completion.
I have followed the procedure(s) described for at least a couple of decades with no problems; I don't have any experience with other developers.
Konical