Recently I have been looking at the very early tax records for Chester County and found that both John Alexander and Gabriel Alexander appeared in New Garden Township, Chester County in 1721. Other surnames known to be associated with the Alexanders who were also present were Abraham & Josiah Emmett and William Gillespy. Actually, the Emmetts were taxed there as early as 1719.
Later New London Township and London Britain Township were formed from New Garden and then John Alexander appeared in London Britain (1725) and the Emmetts, Gillespies, and Ninian Steel appeared in New London. None of them were taxed in the old New Garden Township after that.
I believe it was also 1725 when Zechias (many spellings and misspellings!), known son of Gabriel Alexander, first appeared on that same tax list with Gabriel.
Much later, in 1785, Rebecca (Alexander) Emmitt, wrote her will and mentioned her nephew, Josiah Alexander, son of Gabriel. So I would imagine that her parents, John & Susannah, named a son Gabriel after this man who first appeared on the tax rolls along with John in 1721.
When you were looking at records in New Munster, Maryland, did you also see Abraham Emmett there? Or Gabriel Alexander?