John Colapinto, "When I'm Sixty Four",
New Yorker (4 June 2007), pp. 56-67*:
"...Both men [Carlos Bonell and McCartney] picked up guitars and prepared to work on some passages [from McCartney's ongoing guitar concerto] that McCartney wanted to refine. But first he played the opening bars of a Bach Bourrée. He said that he and George Harrison used to play it together as a 'party piece' in the early sixties. He showed how one of the chords had become the opening notes of 'Blackbird'..."Guess which Segovia's album launched in London in 1964 contains that Bach Bourrée??
IMHO, this is the album Harrison came across with in 1964, the one that 'prompted him' into classical guitar playing at those days**, and the one he sent to Segovia in London to be signed...
Best!!
Xosé
*
This interview was held at McCartney's Mill Studio in Sussex the very day this video was filmed...**
As photographic evidence and his own words at -at least- six interviews let conclude...