1983 should be from the stock of finished ebauches that Blum bought from Zenith after Vermot brought them down from the attic. The movement should be marked 3019PHC, with 40.0 coming in 1986 and 400 a year or so after that. It may be a service movement from later, of course.
Mine has a 40.0 and a 1911 bracelet, which was a novelty in 1986.
—Rick