After six months of scratching my head and trying adminfix.php and lost.php scripts to restore admin rights, Natalio's post put me on the right track. The code fixes recommended were only allowing partial restore (ability to edit the front page).
I was able to comb through the mdl_role_* tables and finally found the two entries on the admin userid that were causing the override (were not set to roleid 1) worked. I logged out of the admin account, logged back in and permissions had been restored. I was then able to go into Site Admin > Users and correct the override that was affecting my co-administrators.