Is it possible that the wrecking crew did more for the Beach Boys then is credited? Is it possible that the Beach Boys are given credit for playing something they didn't play? How do we know that the documents are correct and not the claims of the wrecking crew?
Its generally not documents that support the fact that the Beach Boys played on the majority of their sessions...its the audio evidence. When you listen to raw session tapes, you can hear who is on the floor, you can hear Brian or Chuck Britz talking to who they are setting levels for. On something like Don't Worry Baby you can hear Chuck dialing in the drum intro with Dennis, on Dance Dance Dance you can hear him getting excited about the snare sound Dennis is getting as the session begins. These verbal exchanges between musicians and engineers, while the session is underway, are the best way to ascertain who is there and playing the instruments. Often documentation is just a redundant piece of information confirming what you already know by listening to the session.