From: Rabbi Moshe Sofer
To: Rabbi Shlomo
When a defective Sefer Torah became indistinguishable from valid ones, the Chasam Sofer rejects permitting Torah reading via bitul b'rov, since a Sefer Torah is a davar chashuv that cannot be nullified. He endorses the Beis Lechem Yehudah's approach of permitting reading after exhaustive searching on the basis of a sfek sfeka — perhaps this is not the defective scroll, and even if it is, perhaps the error is not in the section being read.
Source: Shu"t Chasam Sofer YD §277