I had a friend who used to date Kirk Hammett's sister after the Black Album exploded... he's the guitarist in Metallica, for those who don't know.
Anyway, she would house-sit for him and take care of the place while he was on tour and they would stay there a lot.
I have no idea if this is true or not... and I'm certain he was exaggerating a little bit, at the very least... but he said that UPS and FedEx would make daily stops at the house and just drop off boxes of free shit.
Food, clothes, guitars, amps, effects... anything you can imagine... people just sending him stuff for free, with hopes that he'll like it and talk about it in an interview or have his picture taken using it or wearing it or whatever.
An assistant would sort through it all, figure out what stuff was actually Kirk's, decide what stuff Kirk might be interested in... and then just give the rest away to friends and local charities.
My point is... if that story about Kirk Hammett is true... can you imagine all the people who are lining up to give McCartney free shit?
If Dan really was trying to give him that bass, my guess is that he was one of dozens of bass builders trying to give Paul a bass, and Paul probably had no idea.
There's my story for the day.