Great comments fellas, but allow me to make one correction. What studios did in the 60’s (and not just the early 60’s, but all the way through the decade, stereo LP’s not becoming standard until ’68 or so), was not record two separate sessions, one for monaural and one for stereo, but rather simultaneously recorded each session on both a monaural recorder and a multi-track (whether 2, 3, 4, or 8). Doubling the recording time would have been far too expensive to do otherwise. The best studio musicians are paid up to triple scale, and a room full of them adds up to a lot of money! Not to mention the studio time itself (even in the 60's, more per hour than most people made in an 8-hour day), as well as the engineer, assistant engineer, and the recording tape itself, which ain’t cheap. A 10-1/2" roll of tape running at 15ips (the standard in the 60's) records only about a half hour of music, at 30 ips half that.
The resulting monaural and stereo LP’s in some cases can sound like different takes, as the stereo mix may contain parts not included in the monaural mix (mono mixes are done "on-the-fly", not in post-production). Even the mono and stereo versions of the same recording of some Beatles songs contain different guitar parts, making them sound as if they are different takes. They aren’t. Now, some of the 1960’s "live-in-the-studio" Jazz albums DID contain different versions of some songs on the monaural and stereo editions of the albums, but that was a result not of mono/stereo sessions, but only of different takes from the same session.
