Does anybody know why the original version of this song was replaced on later pressings of the LP and later on the CD with a different recording?

mistake I think.
there were 2 released recordings, one 3- and one 5-minute long.

Originally, the 5 minute version was released on the UK album, Rolling Stones No 2. The three minutes version was released on Rolling Stones Now!

However - and rather bizarrely - the 1986 edition of the Rolling Stones Now! features the longer UK version, despite the track length in the sleeve notes referring to the time of the shorter version!

Was the above mistake rectified for the '02 remaster?

I don't suppose anyone out there has heard or even got a copy of the supposed 15 minute version that Roy Carr talks about in his book?

The version that originally appeared on the US album NOW! appears as a bonus track on the SACD version of MORE HOT ROCKS so both are currently available.

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Glam Descendant
The version that originally appeared on the US album NOW! appears as a bonus track on the SACD version of MORE HOT ROCKS so both are currently available.

Ok - but why did they not just rectify the situation by putting the shorter version on the Now! remaster? They should have then put used the longer UK release on More Hot Rocks. They rectifed the problem with Time Is On My Side - guitar version being on '89 Singles Collecection - but not this?

Well not really an answer but when NOW! was reissued on vinyl in the late 80s the shorter version was replaced by the longer version, and the CDs followed suit. I believe it was generally thought that the release of the shorter version had been an error in the first place but have no source at hand to cite.

In short, if you're looking for consistency in this sort of decision-making process you're probably not going to find it, from ABKCO or otherwise.