I like this question, so I pulled my "American Capital Records LP", The Beatles, Yesterday And Today - and listened...The Vocals are on the right channel, and the music is on the left according to my original Capitol recording LP from 1966 or 1967, I believe. You must be listening to the Rubber Soul CD or "the import" European LP, which I believe has tunes from the US Yesterday and Today LP and the US Rubber Soul Lp - not that it matters, but I believe the European LP's, or "the imports" were arranged different from the US LP's, back in the day.
As should the vocals be in the left or right channel?.... I think the vocals should be right down the middle - unless the lead vocalist in the group sets up on the right or left when they preform live, then I think the vocals should be paned to the right or the left slightly in the recordings - but the recording technique was very limited in the sixties from what it is today...stereo was fairly new, and maybe George Martin and the Beatles liked that kind of musical separation (vocals on the right, intruments on the left) in the mix and went with it...A lot of their songs were recorded that way back in the day... I'm ok with it.
As should the vocals be in the left or right channel?.... I think the vocals should be right down the middle - unless the lead vocalist in the group sets up on the right or left when they preform live, then I think the vocals should be paned to the right or the left slightly in the recordings - but the recording technique was very limited in the sixties from what it is today...stereo was fairly new, and maybe George Martin and the Beatles liked that kind of musical separation (vocals on the right, intruments on the left) in the mix and went with it...A lot of their songs were recorded that way back in the day... I'm ok with it.