Ah, thanks Danielle. I'm looking for ways to politely "cut" above the last known generation because these unsourced lines are really a problem.
I'm looking at the ancestors of Langlois-52 (Guillaume Langlois, father of Noël), and find that the people set as his parents really existed in the 18th century in region Champagne, not found his grandparents yet, but his great-grandparents actually married at Cancale in 1798 in 1800, and I have found the marriage of his great-grandmother's parents in Champagne as well, but in 1784.
Go figure.