I think I was reading / seeing on line (or is it in this months record collector) something about a solo Paul McCartney recordings in the 1960s that never got release, dont know if it does exist. Of Course in the 1970s members would sometimes play on others releases, as well as collaborating with other artists in the same way as the Beatles had brought in the odd uncredited and credited (such as Billy Paul) artists in there recordings as well as the production element. This was not often done, I suspect not because they did not want to work together as such, but a deliberate decision to (a) make their own musical styles driving forward, and (b) to ensure fans DID NOT have expecations of a re-formation of the foursome, (and probably demand the oldies). In other words they deliberately did not go down the chicken in a basket caberate circuit of other 60s bands, nor the re-recording of material with new line ups under old names to get new royalties for the latest label one or more members had signed to. Pity in a way, Beatles doing Disco might have been interesting.

Paul wanted to prove he could have success with a group of relative unknown performers working with him in a new group with new material . Ringo went back on later performing to give equal relevance to his work in Rory Storme and the Hurricances, George had the happiness with working with other 60s and 70s greats before his early death. John seemed to bounce off his influence with Yoko again argueable robbed of further new material that would have flowed around his brain.