Roger:

You are right in so many ways. But in the early days, the Beatles did play their instruments. In fact, it's probably the case that they played on those things that were later distorted and added to. But, like everything, there were no hard and fast rules. Yesterday was P McCartney and a string ensemble. Got to Get You Into My Life had some killer brass. Eleanor Rigby was all the members plus a string quartet and Yellow Submarine had a brass band. But the Beatles were the creators of their music, even if they needed pro musicians to realise their ideas. They were the causative element, and they dicided when what they were doing needed a choir, or a sitar or a Binson echo unit, or the whole thing playing backwards. The producers were the equivalent at Motown. Earl: 'A producer would come in, humming some shit...'. The Funks would convert it into something musicians could read or play, and the Motown machine would make sure it was a killer record, regardless of who was on it.