... and the main resolution for why there was no QC HTML appearing is something I should have noticed at the start: there was no "regress" block in the afni_proc.py command. The QC HTML only gets created if the regress block is present. So, even if you don't have plans on using those regression modeling outputs, it would still be good to include it, to have the convenient QC HTML for reviewing things (and maybe even still reviewing the regression aspects, for QC if not for usage).
--pt