Windows 3.1 build 043e

Windows 3.1.043e is the official Beta 2 release of Windows 3.1. Until it was leaked on BetaArchive in 2014-02, it was commonly believed to be a typo of build 3.1.034e, which was already leaked. This build has a revamped Setup and Reversi has been removed and replaced by Minesweeper.

It is also mentioned by internal Microsoft e-mails from late 1991-08, as well as build 3.1.061d's  file.

Another e-mail from late 1991-12 discusses sending "WFP SDK 1.0 Alpha (Kanji version)" and "WIN3.1 Beta2 (Kj)" to IBM Japan. It is unclear whether Beta 2 refers to this build (suggesting there is a Japanese version of it as well) or some other build from Beta 2 stage.