From: Rabbi Moshe Sofer
To: Unknown recipient
The Chasam Sofer rules the woman is permitted to remarry, rejecting the local Gaon's position. Childhood observations reported by adult witnesses do not constitute valid testimony, and since the husband was married with no known brother, witnesses cannot retroactively create a prohibition. He also rules that a mother-in-law is not believed to anchor her daughter-in-law by claiming a yavam exists.
Source: Shu"t Chasam Sofer EH I §42