If you do a search on “Somerset County Genealogy”, you end up finding this page on familysearch. And the important take home is that Somerset County, PA, did not exist before 1795. Before 1795, these lands were part of Bedford County.
Now, since “our” Charles Myers was born in 1789, he could not have been born in Somerset County, as it didn’t exist. Bedford? maybe. Somerset? no.
We have the same issue with folks who want to assign William Myers Sr to Somerset County in 1770. Somerset doesn’t exist, and neither does Bedford. Bedford came into existence in 1771. At that time, those lands were part of Cumberland County.
For those who speak of William Myers Sr (born anywhere from 1735-1740) being from Northampton Co PA (later Lehigh) we run into a similar issue. Northampton County doesn’t exist until 1751. Before that it is Bucks County.