[James2001]

Was it skipped because it's wiped? That would also explain BTTF using a different episode.

No, they all exist, and always have. I think BTTF chose the episode they did because it's the most famous one, and it sets up Marty pretending to be a spaceman later in the film, even if it wasn't historically accurate. I don't know what the reason behind the BBC not showing it was, but it's always been there on the various VHS, DVD and Blu-Ray releases over the decades.

American networks seem to have been reasonably good at keeping their television, prime time at least (daytime stuff on the other hand...), also helps that they made large amounts of content on film, which you obviously can't physically wipe and re-use, plus even the live stuff had to be recorded so it could be time delayed for the west coast (either that or performed again 3 hours later- though that did happen sometimes as well), so it's not as if it went out live and unrecorded and was gone. Though even large amounts of late 50s and 60s VT survives of US TV which as we know isn't the case here, with very little pre-early 70s VT surviving. Most major US primetime shows from the 50s, 60s and 70s have their complete runs surviving, which we know isn't anything remotely the case here.