unless its something like we've seen with Friends, where the best known versions were 4:3 for years and then 16:9 versions have just spontaneously appeared.
It's not really spontaneous, it was a quite major remastering project that took place about 9 or 10 years ago, going back to the original film and scanning it in 16:9 and HD (and having to re-edit the whole show from scratch as a result, as the old masters were 4:3 NTSC video). Quite a lot of filmed shows of the 80s, 90s and early 00s have gone though this (before the mid-80s, shows shot on film tended to be edited on film, so making HD masters is a lot easier, as they're able to just retransfer the film reels of the completed episodes in HD).
Keeping Mum was of course shot on video, so such a remastering isn't possible. Chances are most of the original studio tapes no longer exist either.