Thank you very much, Spa_Guru.
I just replaced the thermostat/probe on my ancient Jacuzzi Vectra II model 8800000. The "official" replacement thermostat not only came with a shorter setting shaft (pain in the butt), but has limited my temperature to about 106°F. After just now learning of the Dec 31, 1979 Consumer Products Safety Commission advisory #79-071, I understand what has happened.
Now, thanks to you, I know exactly where the calibration screw is and how far to turn it.
It's folks like you that make the internet useful.
Thanks again.