I looked at some pictures a while back and it seems if memory serves, that the "front bar" layout of the stacks came in about the same time the octave key moved to the neck. Personally I think it's a suboptimal mechanical layout. It may be that theoretically that layout puts the forces from the bar in line with the forces from the fingers (details not known) so as to minimize the effects of keywork wear, but if so it's not working very well; mine has a lot of slop in the keywork and getting the upper part of the lower stack regulated is a basket of compromises so that no one note leaks too very much. What it does do, is to make adjusting the regulation a right pain in the rear. I added adjusting screws to mine some years ago. It also negates the most common fingering for altissimo Bb, because if you put down any RH finger it also closes the C#-venting key up top, which rear-bar mechanisms don't do.
I'll tell you what I see for intonation issues on the 12M that I have:
1) As with so many older saxophones, a small chamber piece plays sharp, and when you pull out to try to get it "sort of" in tune, it throws the scale off.
2) If you're using a very pulled-out MP, I find the following:
- middle E and F are wicked sharp. I open the low C# on held notes to (counterintuitively) bring them into tune.
- front high E extremely sharp, almost not distinguishable from F, but front high F is in tune.
- low Bb somewhat sharp, but low B a little bit flat.
3) If you use a decent sized chamber (I'm using a Meyer, a LInk would probably be similar), the tuning anomalies get a lot better, but they don't totally disappear (would they totally disappear if I used a very large chamber piece? I don't know. I do have a Meyer piece that I enlarged the chamber a lot, as an experiment, but I had to shove it in so far that it created a new set of anomalies, and I didn't pursue the investigation much further.).
4) For the sharp front E, I put a crescent in the high F tone hole, then I raised the high F pad (when using palm key fingering) and now both front E and F, and palm E and F, play well in tune. I have a theory that when those two toneholes were added, they were positioned "by guess and by golly", and the front fingerings were not considered; then when they added the front F key they did not adjust anything. Again, this all plays into the narrative of minimal to zero development on the baritones.
So on the old ones, what intonation anomalies (with a decent size MP) are y'all experiencing?