Henry de Sewell is mentioned in The Publications of the Lincoln Record Society: The Rolls and Register of Bishop Oliver Sutton: 1280-1299. There is only snippet view in google and I’d have to go to the British Library and ask for it to be fetched from Boston to actually read it. There seem to be actually 8 volumes within volume 69 itself, which is very confusing, and I don’t know which volume is which (I think I want page 3 of volume VII but am not sure). Anyway, that has a long list of people, one of whom is
Henry of Eversholt, t. Dunstable Priory
which is more evidence that Dunstable Priory was running Eversholt church at that time. I think the “t” stands for “Territory”.
Page 35 of that book says that Henry is an “unbeneficed subdeacon”.
There is a copy available for £6.80 on Amazon but I am feeling very poor right now 🙁 Actually they have all the volumes of this series in Lincoln library, but even that is 110 miles away, 220 miles there and back, 4 hours driving.
Sewell is near Houghton Regis.