Perhaps a former programmer deleted the revision history when they were about to move into a management role at your organization. I once stumbled upon a manager's name in the history of a 1970's Cobol program which had a goto statement every 5 lines, and it usually took half a day to make a simple change. All of the other similar-looking programs had had their history purged. When I showed the history notation to the manager, the look on his face wasn't nostalgia but fear.