aberdein,
Today I had the opportunity to browse abbreviated transcriptions of Bellingham parish records.
Bapts were 1684-1851. Fortunately there was a surname index in alpha-order.
Bapt 17 July 1698, Thomas CORBIT son of John of Ellingham
Born 30 July 1903, bpt 11 Sep 1803 William CORBETT 2nd son of William, hind, of Reedsworth, Bank Head, by his wife Elizabeth
Born 1 Nov 1806, bpt 25 Dec 1806, John 3rd son of William, husbandman, Reedsworth, Bankhead, by his wife Elizabeth Maugham.
And the above three , the only Corbett/Corbit entries ( and no sign of William's first son.
If the family of your George were "non-conformists" then they would have used their "own" church.
In the same era there was a Roman Catholic and a Presbyterian within the area of Bellingham Parish. Unfortunately I did not have access to these church records.
Michael Dixon