The Mellotron Group

I am sure that this must have been discussed, but I am curious what rights the original Mellotron musicians have/had when they recorded the original tapes. I also wonder about sections of popular music that used actual Mellotron performances (like the beginning Spanish guitar run in Bungalow Bill). The guitarist who performed this could say that he/she performed on a Beatles song! This is obviously a different story than the violinist who played one note for 8 seconds. I would not expect these musicians to get credit for the Moody Blues or Crimson songs\u2026 Where is the line drawn?