George Martin, Norman Smith (primary engineer for the first six albums), Geoff Emerick (engineer for Revolver, Sgt. Pepper, part of "White Album", and Abbey Road) and the four Beatles themselves never took the stereo mixes very seriously until the last few albums. Through the "White Album" the mono mixes were thought of as the definitive mixes. Stereo mixes were done in much less time, and the Beatles themselves, for at least the first seven albums, were not even present at the stereo mix sessions.
With the early albums, the two-track masters were never really intended to be listened to as they were (backing instrument track hard panned left, vocals and misc. other things hard panned right). They were merely an intermediate step to securing a higher quality mono master (i.e. the vocal/instrument balance could be attended to later, during the making of the mono master, rather than taking up valuable time trying to get it perfect during the actual recording of the songs).
George Martin (regarding the hard panned stereo mixes of the early albums):
Geoff Emerick:"People say to me 'it's great to hear John and Paul coming out of one speaker and all the backing out of the other'. I think it's terrible, myself. There's no way I would have agreed to having those records being issued as stereo in that form."
"True Beatles fans would do well to avail themselves of the mono versions of Sgt. Pepper and Revolver because far more time and effort went into those mixes than into the stereo mixes."
(actually, three weeks, versus two and a half days. The Beatles were heavily involved in the Pepper mono mix sessions but did not even bother to go to the stereo mix sessions).
Why? Home "stereo" record players were still rare in the mid sixties. Most people (especially teens) had the simple mono record player units. Later in the sixties adults might have had the one piece furniture style units where the speakers were only a few feet apart. With those types of units in mind, by the time of Rubber Soul George Martin was purposely experimenting with the hard panned stereo mixes to give more separation. But even at this time, and for another three albums or so, the mono mixes were still considered the "real" mixes.
Stereo mixes became the primary (and in most cases only) master mixes after the "White Album".
Couple of other points:
On the two first albums and equivalent singles (recorded on two track recorders), though the idea was to capture a "live" sound (i.e the Beatles playing and singing a song in its entirety), overdubs of some kind (either extra instruments, lead guitar, harmonica, or sometimes vocals) were performed on the majority of the released songs. A fair number of the released songs were also edited together from multiple takes. Only a handful of songs were done completely "live" with no overdubs or edits (eg. "Twist and Shout"), and on a few (for eg. "Love Me Do" and "She Loves You"), an instrumental backing track was recorded first, then vocals were sung "live" while listening to the backing track being played back on monitor speakers. As they were singing, the vocals and pre-recorded backing track would be blended together through the mixing console on to a second two track tape deck. This process was called "superimposition". The decision of whether to do a complete take, including vocals, or to do it in pieces was usually decided by George Martin, depending on the difficulty of the song, and how familiar the band was with it at the time of the recording. In some cases (eg. "Money", I Wanna Be Your Man" and a few others) multiple superimpositions were done, but usually George Martin tried to limit it to one.
After the Beatles started recording with 4-track recorders (at the time of "I Want To Hold You Hand"), they had a bit more flexibility in adding overdubs, but still they always started with getting a good "live" backing track, sometimes with, and sometimes without vocals. When more than four tracks were required they would do "reduction" mixes, combining several tracks from the original 4-track tape onto one track of a second 4-track machine, and then adding more overdubs on the remaining three tracks. Sometimes (especially during Sgt. Pepper) they would do several "reductions". This is how the Beatles recorded until until mid way through the White Album, when they acquired an 8-track recorder.
One other thing: I don't know how many times I've read statements like this online:
"For 500 dollars the average kid with a computer can have a much better recording studio than the Beatles had"
This is simply ludicrous. While it's true that 500 dollars can buy you a basic amateur digital recording program with lots of tracks and multiple "bell and whistle" effects, this does not ensure a great recording. Any professional can tell you that the "front end" of recording is critical. At the time of recording the Beatles EMI studios at Abbey Road had extremely fine (and expensive) microphones, preamps, tape recorders and processing equipment, plus great "spaces", and of course, expert technical personnel. While tape hiss could build up a bit in the analog recording world (especially after multiple superimpositions), it was barely noticeable when handled by experienced pros. Whether it's the Beatles, or, for example, the great performances of Frank Sinatra in the 50s and early 60s, the quality of recordings from that era speak for themselves. There is a LOT to be learned from the warmth, naturalness and character of those recordings. The best studios in the world today spend hundreds of thousands of dollars trying to get hold of equipment that has that terrific vintage sound.
It's interesting to me as a musician/engineer/producer that for those of us who adhere to the "classic" philosphy of recording a band, the basic process hasn't really changed much. We still begin by getting a good live backing track, then add to it with additional "overdub" tracks, fixing/editing as necessary, and adding some effects for "flavor". Granted, with digital technology and many more individual tracks available, the overdubbing and editing process is easier and more surgical, but the approach is still the same.
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