« Reply #3 on: Wednesday 30 August 17 10:32 BST (UK) »
Nice idea but I think the 3xGGF shared by you and Miss B is probably too far back to be able to definitely rule out that line.
We each inherit roughly half of our DNA from each parent, so there's half we don't inherit. Go back to grandparents and there's three quarters we don't inherit. Extrapolate to 3xGGF and that's a very big proportion of his DNA that you won't inherit and you are very lucky to have got a DNA hit with someone who has inherited sufficient of the same tiny sequence of DNA as you have.
In theory (although I don't know if it's ever happened in practice) and if I understand correctly, you and a full sibling could have no DNA commonality except for your X/Y chromosomes.
If you and Mrs A have both worked all lines of your trees back to 4xGGP (to give you the six generation link suggested by Ancestry) and there are no names or locations (illegitimacy) common to both then you should start looking for multiple relationships further back.
Jane :-)
ALLEN
BARR, BARRATT, BERRY, BRADLEY,BRAMLEY,BRISTOW,BROWN,BUGBIRD,BUTLER
CAIN,CARR,CHAPMAN,CHARLES,CH*LTON,CHESTER,COCKETT
COLLASON,COLLYER,CORKERY
DARLING, DENYER,DICKERSON,DOLLING,DURBAN
FARMER,FURNELL
GIBSON,GILES,GROOMBRIDGE
HALL,HAMBIDGE,HARMES,HART,HICKS,HILL,HOLLOWAY
JACKSON
K*AT*S
LANCASTER,LINTON
MCDONALD,MCFADEN,MEARS,MILLARD
NICOLAS,NOAK,NORTH
PARFIT,PORTER
RIPPINGALE,ROBINS
SEARLE,SPENCER,STEDHAM
TYLER,TILLY,TUCKWELL
WADE,WAGER,WALKER,WATSON,WEBB,WITHRINGTON,WOOD