The usefulness of commands will depend on the environment your game is running in. Here’s what I think for a game running in a web browser.
QUIT indeed doesn’t make any sense, you can safely leave it out.
It might depend on the game, but I think a RESTART command often remains useful even if the game also restarts if you reload the page. On a side note, I think reloading the page shouldn’t restart the game but rather resume where you left off.
PRONOUNS doesn’t feel important to me as a player (it might be useful for debugging but I’ve never felt the need for it).
I didn’t know of the CLEAR command so I wouldn’t miss it.
I recently added VERSION to my own game after beta-testers tried it, but I’ve never felt a need for it (though if you’re distributing the game in way that can leave several versions in the wild it starts making much more sense).
I think UNDO is considered a requirement and players will probably be quite cross if it’s missing.
AGAIN (G) can be quite useful (depending on the game) and would probably be expected to work.
OOPS (O I think) is not something I’ve ever used or implemented in my games but I think some people still use it.
ABOUT / INFO / CREDITS should also be recognized but it’s fine if they all show the same message as HELP.
HINT should at minimum apologize for the lack of hints.
SAVE [slot] / RESTORE [slot] if your game supports it.
As far as I’m concerned the verbosity commands (VERBOSE / BRIEF / SUPERBRIEF) belong to a bygone era and can be omitted but I wouldn’t be surprised if others disagree.
EXITS is nice to have but I don’t think people will get up in arms if it’s missing.
SCORE (and maybe FULLSCORE) if your game is scored. NOTIFY [ON/OFF] I’ve never felt the need for.
A TRANSCRIPT / DUMP command for getting a transcript if very useful.