Windows NT 3.5x/3.50.683
This build is referenced in the NETWORKA.WRI of NT build 854. Nothing else is known other than the fact that it was the official beta 2.
5.25" boot disk images for this build can be found on BA FTP server in the (Misc) Uncategorized/Misc folder. The other available copy of this build has 95% of disks, excluding boot disks, damaged and is unusable.