Yeah that's part of my problem with it, actually! Jaco had giant double-jointed hands. The fingerings he teaches for scales, are simply not practical for the vast majority of bassists with average-sized hands and non-double-jointed thumbs. Too many beginner/intermediate players stretching out their hands and injuring their thumbs and wrists, trying to be like Jaco. The "super stretchy" exercises are preposterous and it was irresponsible for Jaco to include them in the video. In my opinion of course!

I actually slightly prefer Jerry Jemmott's left-hand technique, and wish Jaco had given him more screen time in the video. My hunch is Jemmott is probably a better teacher.