Although Oliver was the 1st Baron, apparently the title wasn't recognized as hereditary because the next Dinham who was recognized as a Baron was John, dsps. 28 Jan 1500/1. Apparently, according to CP, a committee in 1914 found that the barony did not exist from 1299 to 1466/7 when John was created the next Baron, although CP thinks that the claimant's legal representative mishandled the case.
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Constable of Exeter & Taunton Castles. [Ancestral Roots]