I would like to correct a major error in my original post. Archibald of King George did indeed have a son Archibald. This Archibald Jr. appears to be the same Archibald Allen who married Abigail and settled in Fauquier.
The author of the abstracted will I had initially consulted had errored in the omission. I should have mentioned this months ago. I hope it hasn't cause too much confusion.