Metallica's page is locked, so I couldn't add them. Surely, lots of people know that they put out three demos (the Whiskey Audition tape, the '82 garage demo,
and Power Metal), so why aren't they there?

Never publicly released via official band-sanctioned sources. The ones you hear and that distributed are bootlegs.

there's a chance I've mixed memories, but Power Metal was distributed by mail, according to "Metallica: Enter Night: The Biography". I don't have a copy with me, but I'm leaving this here as I suspect quite some ppl on this forum might have it. if I recall correctly, there was even an interview with the early fan who handled the posting, on behalf of Lars "never too soon to outsource" Ulrich...

I believe the "Power Metal" was officially released as a demo tape and should be included, as it was distributed both to promoters and to underground fans. I've read this from more than one source. (McIver's biography as well as Ken Doughton's.) It was not as widely distributed as "No Life to Leather" but still, it was made available via the band's small, secluded network of fans at that point in time. I would agree that it is not necessary to list every rehearsal recording made during that period, but I think it is appropriate to acknowledge "Power Metal" and "No Life Till Leather" as equally valid releases.