@rocky chains
I do know the basic story, but I may be missing some specific details.
The Agora in Cleveland regularly recorded many of the bands/artists who performed at the venue and would then broadcast the tapes on WMMS FM. That is why we have three different performances archived of Rush at the Agora, all originally recorded from the soundboard. The bootlegs that have been circulated for decades were sourced from a fan's home recording of the broadcast from the 1970s. In the year 2000, the Agora master tapes were dug out and rebroadcast for the first time in 25 years. A Rush collector friend of mine who experienced this rebroadcast told me that when Garden Road started playing, it blew everyone's mind, because apparently no one had ever heard it before (unless you were at a concert) nor expected it. What he theorized is that either, a, Garden Road was omitted from the original broadcast, or b, the taper of the home recording missed capturing the song for some reason.
I do believe the December 16 Agora show was also rebroadcast around 2000, but I'll have to ask about that at some point to confirm. Either way, the master tape for this show was also recovered around this time, so these two 1974 Agora shows managed to get a proper digital transfer from the masters, I believe by some fans who were into Rush bootlegs/collecting. Again I'd have to confirm the exact details. For both this August 26 and the December 16 recordings, my recommended downloads and the ones labeled "Sirius Master" are those versions direct from the master tapes.
Unfortunately the master tape of the Agora show from the FBN tour on April 7 of 1975 appears to have been lost forever, but luckily some fan did at least record the broadcast in the 1970s. My theory about that show is By-Tor seems a very odd omission from the actual setlist, and that perhaps the master tape would reveal the song was only omitted from the broadcast to save time. Sadly we will never know (unless by crazy chance an audience recording pops up). From what I think I recall reading, a lot of the Agora's master tapes were destroyed in a fire at some point before 2000, which is why some could not be recovered. I need to double check those details as well, because I recall another instance where master tapes were destroyed in a fire, those recorded for the King Biscuit Flower Hour (they recorded Rush in Toronto Sept 11, 1974, but the recording has been long lost to time).