Microsoft never used SourceSafe for anything important internally.

Hmm. Not sure I agree. The initial CLR for .net was in vss. Maybe it wasn’t important, but bonus points if you know why.

No definitely not true. It was in Source Depot if not SLM.

This I can believe.

Personally, I enjoyed MS source safe and exclusive file locking.

I loved SourceSafe for the disappearing files, and the usual "John locked the file and he went on holidays."

Well that was just bad manners and you could force unlock.

Perforce also did exclusive file locking (and I believe Microsoft ended up using a customized Perforce internally at some point).

sd was a light customization of p4

https://devblogs.microsoft.com/oldnewthing/20180122-00/?p=97...

Did SourceSafe even have a proper merge?