[Even thought we heard back from our researcher in Wales that the 5th piece is inoperable as a strange coincidence of names (it was a different village, different mother, and apparently a different "Rees Price"), we still think the first four are enough. We'll keep looking, but we may never find anything more solid.]
It's still only a circumstantial case, but all the pieces fit. Here are the parts. You can tell me if you think we got it wrong.
1. 6 March 1789, John, bastard son of Hannah Vaughan, christened in Hay, Breconshire.