Zero downtime deployment with stored procedures should not be confused with "version control".

It's not a version control scheme; once deployed the procs are never updated.

Yea, I suppose backwards compatibility is really the best policy there. If a proc is going to be updated to be more efficient it's one thing. If it's going to change what it does then we just need a new proc.

Yep. (if there are schema, changes too, zero downtime & backward compatability is difficult to pull off, but thats a chore for any strategy )