The early alpha builds do not have a registry, thus I wonder what build was the first to include registry?
Build 196 (the first release outside Microsoft, September 1991) doesn’t use the registry, although it does create a
C:\REGISTRY directory when running.
Build 297.1 (the first public beta, July 1992), compared to build 239 (December 1991), drops
REG.DAT (which is presumably a Windows 3.1-style registry) and adds the registry editor (
REGEDIT.EXE) and a
REGISTRY.INF which is probably registry-related. So the Windows 3.1-style registry was added somewhere between builds 196 and 239, and the NT-style registry somewhere between builds 239 and 297.1.
Build 404.1 (the second public beta, March 1993) adds