The northern songs stock buy-back was from the book "Apple to the Corp". I think it was corraborated in the Playboy interview with Lennon.
After Linda's memorial service and the snubbing of Yoko, Paul said in many press reports that one of the reasons he snubbed Yoko was that she told the press ..."Paul did more to hurt John than any person in the world"..
John was quoted in Lennon remembers with Jann Wenner or with David Sheff in the Playboy interview that "Paul would subconsciously ruin his songs"
Like many of us, i sort of grew up and learn to read while reading the stacks and stacks of books and interviews on the Beatles, probably the most publiciized band of all-time. So, i'm fairly certain what i wrote is backed - up by the books and many other sources. Somebody like Mike who runs this site is probably a lot more knowledgeable than me on this stuff but i'm pretty sure i got those quotes right.