SCCS (Source Code Control System) - http://en.wikipedia.org/wiki/SCCS

It was originally developed at Bell Labs in 1972 by Marc Rochkind for an IBM System/370 computer running OS/MVT. (cited)

M. J. Rochkind: The Source Code Control System. In IEEE Transactions on Software Engineering SE-1:4 (Dec. 1975), pages 364–370.

This Paper also contains some references which might also be useful as Prior Art, remember to come back to those if we can't find anything here

CiteSeer is very helpful in finding Documents that refer to this one, so remember to come back to those if we can't find anything here: http://citeseer.ist.psu.edu/context/7732/0