Coldham's "Settlers of Maryland 1751-1765" lists a James Mattingley in St Mary's County, 372 acres, name of tract "Mattingley's Slipe" 10 Feb 1762. (ref.BC17/404;BC19/544). The book also lists the same year (2 Sep 1762), a John Baptist Mattingley buying 46 acres "Grave's Swamp" in SMC. (RefBC16/403,BC19/248). Maybe these were the James and John of Charles Co..?