It's worth your time: "Come Together: The Night Lennon and McCartney Reunited"
“Valiant Paul McCartney, I presume?” said John Lennon. “Sir Jasper Lennon, I presume,” responded Paul McCartney.
Such was the manner in which the two former Beatles greeted one another when McCartney showed up, unexpectedly, at a recording session Lennon was conducting on March 28, 1974. In the throes of his “Lost Weekend” period, Lennon was in a Los Angeles studio overseeing production of Harry Nilsson’s Pussy Cats album. Present were a number of players – including Stevie Wonder, guitarist Jesse Ed Davis, saxophonist Bobby Keys and Nilsson himself. McCartney was accompanied by his wife, Linda. Lennon’s then-girlfriend, May Pang, was there as well.
. . .
Pang went on to say that McCartney seemed not to want to entertain the thought, perhaps because the idea of such a missed opportunity was too painful. A year later, however, at McCartney’s annual Buddy Holly tribute party in New York, the former Beatle rushed over to Pang as she was talking with Linda McCartney. “Tell her!” McCartney said. “Tell me what?” said Pang. “One of Derek Taylor’s postcards from John fell into our hands,” McCartney said. “John had written, ‘Thinking of visiting the Macs in New Orleans.’”