Mr Red, do you have any evidence to support your allegation about Paul McCartney?

It's true that a lot of PRS royalties don't get distributed, that's because a lot of musicians don't submit a claim. Which reminds me...

If a songwriter sells his song to a publisher he then loses all control over it. Presumably the songwriter was happy with the price he was paid, if the publisher then decides it's not commercial and doesn't release it that's their loss.