Yes, yours is the most likely scenario. However, IF the original records were that Peter WAS born in 1748, it would pretty much rule him out as the husband of Priscilla Waugh, and mean she married another Peter, since I can't believe that a 21 year old woman would have married a 14-15 year old boy. It might also explain why Peter did not seem to be second in line in the will of Peter dated 1750. This is why I need to get to the original record in Va. State Library in Richmond. If Peter was born in 1748, then the Peter born in 1730 would be her likely husband, UNLESS there was yet a third or forth Peter around.
However, another plus for your scenario is that in the will of Peter that died in 1750/51 is that the witness Peter in that will must have been of age. At 20-21, the Peter born in 1730 would fit this scenario.
In sum, if the original Overwharton records make it clear that Peter was born in 1748, it would pretty much rule him out as the husband of Priscilla. However, even if they do support the 1738 birth date, it is still not proof, as you say. It would take more evidence, i.e., other wills or deeds linking the family lines, to prove it.
This is where Armand Mauzy was also confused, but he is often quoted.
He originally published that Priscilla Waugh married the Peter born in 1730 to John Mauzy and Hester Connyers. After my mother wrote him, he responded to her, and indicated he didn't have it right, and gave her his new idea shown in this link: http://genforum.genealogy.com/mauzy/messages/263.htmlhttp://genforum.genealogy.com/mauzy/messages/263.html
But the changes appear incorrect, also. He kept the marriage the same, but changed the birthdate to 1738. He also added a Peter of 1748 as the son of Peter who died in 1750/51, and said this Peter married Elizabeth Buzzard. This is clearly wrong, as the Peter that married Buzzard was born around 1765, and is said to be a grandson of the Peter who died in 1750/51, and son of Peter born 1738, the likely scenario. Curious that Armand now has dates of 1738 and 1748 for different Peters. My hunch is that he saw both books that transcribed the Overwharton register, and made the mistake of seeing this Peter as two different ones, and force fitting them into his "corrections". He used the 1738 date to change the 1730 birthday of one Peter, perhaps because he assumed that the 1730 birthdate was a typo or gained from unclear handwriting. However, I don't know where the original 1730 date came from. It is just out there with no supporting evidence. It may have come from Richard Mauzy's book. I haven't looked at it in a while. But if it did, there was no factual support for that date, and Richard had some incorrect info in his book.
I note also that Tyler Waugh, Priscilla Waugh's brother, married Margaret Waugh, said to be born in 1738. Not impossible if her brother Peter was born in 1738 instead of 1730, but a red flag to Armand's "corrections".