"with those three four-measure call and response phrases" Normal 16-bar blues had four four-measure phrases. I don't understand what the significant difference is supposed to be between normal 12-bar blues and normal 16-bar blues with regard to "possibilities for creativity and improvisation."

"16-bar blues (often also written as 8)" I wouldn't say I-I-I-I-IV-IV-I-I-IV-IV-I-I-V-V-I-I tunes are often written as 8-bar.

"I just finished listening to some old Sidney Bechet and Louis Armstong cuts, comparing their work with 12 and 16(or 8) and they both understood the differences, and used them to excellent effect." You listened to Bechet and Armstrong playing 16-bar blues? Which ones?