You really do need to know your history to accurately use place names on the American frontier. "Six counties—Washington, Sullivan, and Greene in East Tennessee; and Davidson, Sumner, andTennessee County in Middle Tennessee—had been formed as western counties ofNorth Carolina between 1777 and 1788." (Wikipedia, History of Tennessee). These six, plus two other counties in present day Tennessee, formed the State of Franklin, which ruled the area from 1784-1789, though it was never recognized as a State. So officially, they would still be North Carolina births/marriages/deaths. In 1789 with the ratification of the Constitution, North Carolina ceded the lands to the Federal Government, which named it the "Southwest Territory." In 1796, Tennessee applied for Statehood and became the 16th State.
The counties of present-day West Virginia were all part of Virginia until the Civil War; when they did not want to join the Confederacy, they ceceded from Virginia and became their own state in the Union. Some county names also changed. So dates of birth, marriage and death before the Civil War will be in different states than dates in the same places after the Civil War.
Should genealogy follow these changes? Yes, by all means -- for genealogy is a subdivision of history. Of course, the narrative can say that these are all places in present-day Tennessee or West Virginia -- but what's the point of doing genealogy if one isn't going to be accurate?