I've encountered the same kind of spelling vagueness.I have a copy of an 1812 Somerset County MD will that is said in the text to be that of "Levin Folling", is signed and sealed "Levin Follin," and then is authenticated by "Henry Fallin" as the true will of "Levin Fallin."All in consecutive entries!
Even closer to your records there's a USGenWeb transcription of marriages in Upson County, GA that first shows Jackson Fallin and Elizabeth Minter marrying on February 2, 1836 and just a little further down has Jackson "Fallen" marrying Hulda Jones April 22, 1858.From other sources I'm certain it was the same Jackson Fallin marrying first Elizabeth and then Hulda.
Unfortunately, I gather from your silence on the subject that your material has no Joseph Fallins.Oh well.
As I think Ken mentioned on the other message board, I have indications, that I haven't yet been able to authenticate, of an Andrew Fallin that preceded the first Charles in your record -- apparently being in Northumberland County, VA as early as 1623.If I can confirm any of that I'll let you know.
After I've digested all the new material you've given, I'll post some of my MD info.