Jack,
All your chewing over is relevant..... except Woodhorn vis-a-vis Seaton Delaval.
There is little chance of Seaton Delaval been written instead of Woodhorn or vice-versa, other than as a simple mistake !
It is not just a matter of the distance between them ( about 7 miles), but what lies between them !
If we just talk "ancient parishes".... from Woodhorn in the north, coming south, we have to go through the parishes of Newbiggin, then Bedlington, then Horton, then into Earsdon. Seaton Delaval was one of the eight "townships" ( a sub-division of a parish) of the parish of Earsdon.
Also up to 1844, Bedlington ( the wider area was called Bedlingtonshire) was owned by the Prince Bishops of Durham, was was regarded as within the County of Durham, and not part of Northumberland.
I hope to help settle this little geographic issue, by browsing parish records of Woodhorn and Earsdon for Johnson bapts
( images of the church records will be available when the Northumberland County Record Office opens end Oct/beginning Nov,,,, in WOODHORN..... but Newcastle Library has some indexes..)
Michael Dixon