Jimmy:
I wouldn't ask you to talk out of school, but I've always heard of session guys being called in to, ahem, finish projects for bands that have gone late, over budget, what have you, when the principals involved can not finish them for any number of unfortunate reasons. I'm generally thinking along the lines of 'The Decline of Western Civilisation, Part 2'.
I often think of certain hair band records, then seeing vastly dumbed-down versions of the same tunes in their live shows. Was this a common thing then, or now? I even heard of guys having to sign confidentiality agreements that they were never there !
J o e y