It looks very much as if there's an overstamp involved . Just above the extreme left pellet is the trace of a cut corner .
Benjamin Bickerton is a possible
7 June 1749
Apprenticed to Henry BICKERTON (his brother )
26 November 1754
Will of his father, John Bickerton of St Giles, Cripplegate proved at PCC
He left the leasehold of a property in Nags Head Court, Southwark to be shared equally between Benjamin Bickerton, and his brother Joseph . Thus he had finance available towards t the end of his apprenticeship
22 February 1756
Marriage of Benjamin Bickerton of the Parish of Saint Mary Whitechapel and Mary Worsley of the Parish of Saint Brides . A little early as his seven years of apprenticeship was supposedly still unfinished, but she may have been thought pregnant , and his brother allowed the marriage !
So perhaps he soon left Henry and set up his own business before 1758 and had a mark in the lost Small Small Workers register