Yes the EBU now have rebuilt the archive of Eurovisions for internal use from different broadcasters off-air recordings, even fan recordings, to build as clean a copy as possible from the different sources.
Why would the broadcaster recordings be off-air? Most UK broadcasters recorded either the output of presentation (the BBC routinely did this for live events) or the output of the studio feeding presentation when making recordings of live shows.
Off-air recording wasn't that common (as it was significantly poorer quality than a baseband recording) - though it was used in some cases I believe.
They even dubbed the stereo audio over from the FM simulcasts where available.
Yes - I can imagine that if the FM simulcast was stereo but the TV broadcast was mono, then the original VT
recording would have been mono (and the radio archive recording stereo).