My 2 cents, fwiw...
I gotta go with Murray on this one.
I think Purdie spoke without thinking at the time, and is just too stubborn, embarrassed, or whatever, to admit it.
I read 6-8 articles yesterday about Purdie's claim, and none of them could find any verification of his story. Some of them did some pretty deep digging.
The nearest they could come is that he MAY have dubbed a few for Pete Best when Atlantic? did a remix of some early cuts, as Murray's article stated.
Ringo, naturally, denies the claim.
Personally, I never thought Ringo was that great. As one article stated 'Purdie could drum circles around Ringo.'