Windows 3.1 build 61d is a pre-release build of Windows 3.1. This build is the "Final Beta Release". It can be found on BetaArchive and other places. It was compiled on 18th December 1991. It is also mentioned is several Microsoft Antitrust documents, e.g. PX01251, which states that final beta was shipped to testers on 3rd January 1992.
