From what I've read about the history of the filming of the series, I find it very difficult if they had done any scenes live. Virtually all episodes were done live-on-tape at least a week if not more, before they were aired. In the beginning, everything was done while filming, from opening credits, to filmed exteriors, to commercials, to even the soundtrack, to the closing credits, all packed in and done. Later in the series, some things were added on after it was filmed. Another consideration would be that if something flubbed so severely earlier (or if something had been lost), was that it would've been necessary for the performers to be on the soundset to air that particular scene. Since they tried to keep the number of bodies - live or dead - down to a minimum, what were the odds that the particular performers happened to be on the set, or to even have the set up? Only a few were permanent, such as the foyer and drawing room, so they would have to get everything suddenly put together and there was very little space to do that.
Gerard