John Purdom II (father of William Purdom who married Mary McBride) definitely died prior to 1800, as his widow is listed as head of household in the 1800 census and there is no John Purdom listed in Surry or Stokes Co., NC of the age to be the correct John. Perhaps the 1824 dead date is for his son John who married Susannah Graham in 1792? Also, John Purdom II definitely appears to be the son of John I, not a William. By tracing land that John II owned, he can be connected to John I who died in Johnston Co., NC in 1762, and court records clearly refer to John Purdom Sr., deceased, and his son John Purdom Jr. As I mentioned, land records point to this John Purdom Jr. being the same John Purdom who was the father of Henry, John, Polly, Elijah, Elisha, William (m. Mary McBride; this is the ancestor you and I share), Thomas, and Marcus/Mark Purdom.
I'd be happy to send you the detailed info I have. Please email me directly at firstname.lastname@example.org if you're interested.