Date: 7 Tishrei 5575
From: Rabbi Moshe Sofer
To: Rabbi Pinchas Leib Munk
When two sheets of a Sefer Torah each lose one invalid column, the scribe proposed consolidating the repair into one four-column sheet and leaving two valid columns as a separate two-column sheet, invoking the Taz's leniency that two columns are valid bedi'eved. The Chasam Sofer rules that the need to avoid sending valid material to genizah does not create a bedi'eved status, since the minimum column requirement is a clear-cut original enactment with no underlying doubt. Each replacement sheet must therefore meet the standard minimum of three columns, even if valid old columns must be consigned to genizah.
Source: Shu"t Chasam Sofer YD §257