I just bounced around and checked a few of the live playing shots.

Yes he did go to the traditional (all sausage fingers,image God bless him) under the valve casings, none under the third valve slide, first when he switched to just his Monette mouthpiece on his Leblanc/Holton MF horn so maybe the Monette mouthpice had a very different feel in some way so he gripped different.

He also stayed with that grip when he went to the full Monette set up, horn and mouthpiece.

I'm sure Sev's point about the arthritis was a factor as well, or maybe the primary factor.
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Just speculating.

Maynard Fanimage