From: Rabbi Moshe Sofer
To: Rabbi Shlomo and Yuda
An unmarried woman who had illicit relations roughly ten years prior seeks permission to marry a Kohen, claiming her partner was a kosher Jew in a predominantly non-Jewish city. The Chasam Sofer rules conditionally: if the man's corroborating admission is available, she is permitted; if her bari claim predates the shidduch, she may be permitted with a concurring opinion; but if she was only examined upon the present shidduch, her claim is suspect and she is forbidden even post facto.
Source: Shu"t Chasam Sofer EH I §18