First, the parents listed are incorrect. I don't know who his parents were, but they certainly weren't Thomas Buckner and Elizabeth Crackplace who married in St Michael's Cornhill, London in 1590. This account of them given here is based on several very bad published sources, one of which created this confoundingly persistent error of giving Thomas Buckner's marriage date as his birthdate. It's remotely possible that they were John Buckner's grandparents but the evidence leans against it.
Second, the John Buckner who married Deborah Ferrers in London in 1661 was a totally different John Buckner, who died in Reydon, Suffolk, England in 1678. John Buckner of Virginia was already in Virginia by 1655.
Third, the death date listed is actually the date of the return of the inventory of his estate. The true death date is unknown, but it was probably in the summer of 1695, since the probate proceedings started in September (Before someone asks, the 10 Feb 1695 inventory date is Old Style, so it's really 10 Feb 1695/6.)