On the original Redd Consoles at Abbey Road Studios they were setup for orchestral recording. They had what they called the "Decca Tree" It was setup not for stereo, but for A, B recording with one mic aimed towards the 1st and 2nd violins (Left) and another aimed towards the Violas,Celli and Basses (Right) and also a center mic. Not for stereo, but to pick up the spread of the orchestra. Those tracks were hard wired to track 1( Left side) track 2 (right side) tracks 3 & 4 on the 4 track were reserved for solo instruments. When stereo was introduced whatever was on track one was normalled to the left side, That's why on early Beatles recordings you hear the first pass, usually the basic track with the drums and Bass panned to the left and their second track (usually the first overdub Vocals or Guitar parts)on the right. At the time engineers didn't know how to treat stereo. Phantom Center hadn't been realized yet. In fact the Beatles usually left when they printed the stereo mix. They didn't consider it important. Mono was king at the time!
