Carole it crossed my mind as to whether you picked up the marriage of 1631 in a banns register rather than the actual marriage register. In general the earliest baptism/ marriage/ death church registers date from 1538 in English churches. I do not know of the history of Welcombe church but possibly the earlier records were lost in say a fire or damaged by damp or pests. I do not know if a banns register did exist and an alternative possibility is that somebody transcribed the entries in a family bible.
John