I've been studying the migrations of surnames you mentioned ( Polks, Brevards, Pattons, Mcknitt, Jackson) and many of them are found in the early Cumberland County, PA records pre-1765.
I'm especially interested in proving their connections to one another as they relate to the Polk surname. It's my understanding just from the land records that most of them originally immigrated to the Cecil County area, then Cumberland Co. PA (which was created from Lancaster Co. in 1751)and then on to Mecklenburg.
Of particular interest, is a Rev. William Smith. I don't know where he came FROM as I've not researched that line, but he made at least ten separate land purchases in Cumberland County, between Feb 6, 1765 and July 1766, ranging in acreages of 75-450 acres each in 10 unrelated areas, indicating in my opinion that he might have been buying land for other people, possibly his congregation members. I'm not thinking it was likely that a minister would have had the funds to make those kinds of land purchases from his own income. The time line of his land purchases follows many Indian skirmishes where some pioneers fled their homes to a safer haven elsewhere, which would explain alot of the migrations to other areas or states.