Jack,
I think I have lost the plot, and many of my notes... but here goes...
On C1861 at Sherriff Hill ( 3806-53-8) a one yr old John is recorded as son of John 61 and Martha 63 child born Coundon.
"3 yr old Sarah Johnson is in h/h as dtr.
On C1871 still in Sh Hill at 5061-65-11 Sarah is now a 34 yr old widow ( married John Drummond in 1865 Gateshead registered.... His death reg at Gateshead 3/89 aged 34.)
Sarah's children are John Drummond 11, Martha Drummond 9, Mary Drummond 6 and William aged 1..
There are no birth regs in appropriate era for a John Drummond, but there are for John Johnson
( Incidentally there is a bith reg in Gateshead RO for a Sarah Drummond, then a death reg in 1868 for the death of a 3 yr old Sarah Drummond ! )
So thast is . I think, why I suggested that John was Saqrah's child and not a child of her parents.
By C1881 Sarah is wife to a John Corbett ( 5041-22-37) with 19 yr old Martha Drummond in Household.
Sorry to have taken so long to reply.
Michael Dixon