I think the dividing line is Revolver, because 1966 was the year that Brian Epstein, who had guided their career from the beginning, appears to have lost control. They stopped touring, and since concert coordination had become his primary function, he didn't have much to do for them, free to engage in his often destructive side activities, including trying to sell NEMS and his rights to Robert Stigwood, which irritated the group immensely. Fresh from the insanity of Lennon's US Jesus remark mania and the Philippines debacle, George announced that he was ready to quit and, judging from the delay in resigning with EMI, so were the others. Note that their five-year management agreement with Epstein expired in late January 1967. When they finally emerged with a new record deal around that time, there was a new dynamic to the group, reflected in their music, which, to me, was not as appealing as what had gone down before. Notably, George had only one song on Pepper's, on which none of the others played. Something fundamental appears to have changed during the months' -long decision to re-up. Things were not the same, from all appearances.