If you want finding old posts with external search to work, you may consider a username change here. Even this site-delimited search string:
site:discussions.apple.com "SU" -command -terminal
gave ambiguous returns. Got some Subaru hits about CarPlay, and one was about an Asus monitor! Both had "su" in them.
Any member with reporting privileges (Level 3 or higher) can sned a username change request on your behalf. A name change affects all you posts, even those you cannot see using internal search. It should not prevent you from web access to old posts.
NOTE: in the site-delimited search string above, note there is no space between the colon (:) after "site" and the "d" in "discussions."