I realize this is an older topic, but it is one that has caused me quite a bit of frustration for decades. My ancestor road block has fallen into a hole somewhere because most information I find on him lists him in a county that was not formed at the time of his birth. I have ran into this many times with other people as well. I often find people listed in a state or county that the borders have shifted over the last 3 centuries in the U.S., which makes it difficult to know where to go to for further research.
Using my roadblock as an example, James Shields, Shields-1830, is often listed as birth location Adam County, PA. According to family documents and military records, as well as headstone, his date of birth is April 14, 1733. On January 22, 1800, Adam County was entered into legislation for formation as a County within 2 presently formed counties. If you pick a spot, say Strabann Township where his father-in-law's will was recorded in 1795, it was part of York County until the formation of Adams. At one point, it was also part of Cumberland and Lancaster Counties, yet I repeatedly find him listed over and over again with birth location as Adam County, PA. At one point, an area of present day Adam County was also part of Virginia!
The next point to search under is the place he enlisted during the Revolutionary War, which was Chambersburg, in the newly formed county of Cumberland County, PA on the date of May 26, 1777. The city of Chambersburg in PA has a rich military history dating back to the formation and settlement by William Penn, and has been located on the Mason-Dixon Line dispute documentations in the Maryland Colony, as part of Chester, Lancaster, Cumberland Counties, but is now the county seat in Franklin County.
From this point on, I can trace James Shields through the battles he fought in, census, land warrants, and military pension as well as documentation of his endeavors in the Indiana Gazette, including his voting precinct. I can locate many individuals born around the same time frame that could be possible brothers or cousins from that same 400 mile radius, but without a finer point of location there are a lot of James, Robert, William and John Shields within that radius! A Robert and John Shields are well documented both by DNA and records, as these 2 brothers became well-established citizens who's parentage was recorded and became literate in their older years. My James apparently did not, nor was his wife, as everything signed was made by 'Mark', tho his younger children were. James moved to Western PA, and John stayed in that area with Robert settling in VA, marrying a prominent family and becoming the father of a Senator. The direct descendants of those 2 brothers have a proven DNA trail to Ireland's James Shields the Elder who's family was disbanded and scattered by Cornwall during the English Campaign, with sons Robert and James captured and enslaved to Barbados, later escaping and making their way to PA in the late 1600's.
So... which direction do you turn when so many, including Family Search and LDS, claim a birth location in an area that did not exist during the dates also claimed? Better yet, how do you end the misinformation out there by so many who keep 'copying' it over and over without digging deeper? I grit my teeth every time I see one of the many I am researching falling into these gaps. I have a Dunlap, Whitacre, Mock and McSwiney ancestor that have fallen into that same elusive time v. location warp that no one bothered to look at a map during the time frame they list for accuracy! With these people, I always list location as uncertain or possibly thus or so in WikiTree, and cross my fingers someone can come up with a better way to dig a little deeper!