I'm not really familiar enough with the music to speak to the different versions musically, but the release chronology is that the first versions were released in the US only in 1973 on CD-4 LP and Q8 when Virgin was still distributed by Atlantic Records. These definitely came out in this time frame, because the US quad version
Ommadawn released in 1975 was pressed and distributed by CBS, I guess Virgin must have moved US distributors by then.
Then in 1975 you get the standalone SQ release of
Tubular Bells in the UK, and finally in October 1976 you get the release of the
Boxed compilation.
What I'm not really clear on is if there's more than one quad mix of the album - all of the quad releases of the album before the
Boxed version have runtimes on the label marked 25:00 (Side A) and 23:50 (Side B). The version on Boxed has the runtimes as 25:55 (Side A) and 25:47 (Side B), and actually makes mention of the added
Sailor's Hornpipe on the label.
In the liner notes for the SACD, Phil Newell recounts the creation of the quad mix (you can find pictures of them in the
discogs entry if you don't own the disc) and says there were some "abortive attempts at an earlier Four-Channel Surround re-mix in Abbey Road" before the quad mix he did with Alan Perkins. The whole thing is worth a read as it's very informative, but he also mentions that the quad version was mixed to Ampex "instrumentation tape" in sections and then spliced together, which would account for the weird spectral readouts of the album.
So I guess there's three possibilities here:
1) the Newell/Perkins quad mix is the only mix, and it appears on all US and UK quad releases, but the Sailor's Hornpipe is excised from all of them except for the
Boxed release.
2) the "Abortive Abbey Road quad mix" was actually released in the US in 1973 on CD-4 and Q8, but the 1975 SQ is the Newell/Perkins mix minus Sailor's Hornpipe.
3) the "Abortive Abbey Road quad mix" is what's on both the 1973 US releases (CD-4, Q8) and the 1975 UK SQ release.
Like I said I haven't heard any of them except the SACD, and the runtime on the SACD is 25:35/23:22 so I'm not sure it even includes all of what's on the
Boxed version of
Tubular Bells.