The cost cutting of Super 20's began in Cleveland, and some changes, such as eliminating the double socket neck, are actually welcomed by some players. The left hand table keys certainly were improved during the Super 20 run, and I actually wouldn't want an early one for this very reason.
If you're looking for something to do, I'd like to see you expound on what characteristic or feature you think is better about the later table keys. After about 384K I think they took a definite turn for the worse, and the octave key mechanism, too.
The very earliest Super 20's had a table key arrangement that was too low (278K - 283K), and then it was raised up about 1/2 inch on the horn.
From 283K - 294K the G# was a flat pearl. Contrary to what many people say, I think this was one of the best designs table keys on all Super 20's, and shouldn't be confused with the reversed hinged models that followed. The pearl octave keys are really cool on these horns, too. This is my favorite vintage of all Super 20's; the low Bb and low B are easier to reach and play than on a Mark VI, and playing from low Bb to C#, or low B to C# is quite easy.
From about 294K - 305K the G# key mechanism was reworked, and I think this one feature has a significant negative impact on the value of these horns, to the tune of about 20 - 30 percent. The G# key on these Super 20's hinges in a funny way and makes it cumbersome to play. The G# key is pearl faced in this range.
Then at about 305K came what many consider the best Super 20 table key design of all, and with full pearls this design lasted until about (350K)? Not sure about when it ended. The roller pearls on this range were barrell shaped, and the G# key had a pearl facing.
The design that followed is also excellent, but doesn't have a pearl facing on the G#. This design lasted until around 384K.
When the single socket necks kicked in, at around 384K, the table keys got wider and more square in appearance. I think people familiar with the different designs generally agree that this style is not superior to the earlier Super 20 table key designs, except for the very first series, and the the range that started at around 295K with the reverse hinge.
I had tenors in mind regarding everything above when it was written, but I believe most of it would apply to altos, too.