because the drummer is part of the Aussie band (possessive)
St James's Park (London)
because it was name after St James the Less (possessive)
St James' Park (Newcastle)
the difference in spelling might be guessed to be due to
- Geordies didn't want a park with the same name as one in London
- The stadium took the name of the area which used "James"
- Geordies don't know how to spell
There is an extensive description of the conundrum here.
Note that there was a time when the stadium was spelled "St James's Park".
in your example is being used as an adjective same as in
United Airlines seating chart
It is "a Beatles song" meaning
The song is (sung) by the Beatles
but it would be "the Beatles' contract" with their record company that got it produced.