Numbered stored procedures: introduction and deprecation?
Looking at the SQL Server 2000 T-SQL help, there is no mention of deprecation so it seems numbered stored procedures were deprecated with the release SQL Server 2005. 

I don't recall numbered procs ever not being in the Microsoft SQL Server product on Windows so I'm pretty sure the feature stems from it's Sybase roots and is in the 4.21a Windows release. I can't speak to the OS/2 version since I dodged that bullet :-)