Hi Alex,
the Ref. 3910 is an absolute puristic model (some named it a "basic model" of the Breguet line) with a black leather strap and a 18kt-gold buckle:
diameter 34,5 mm, handwinding movement, small second, no date or other indication, the full Ref.-No. is "3910BA/15/984" - case yellow gold. It was also available in white-gold with Ref. 3910BB/15/984. As far as I know: Production of the Ref. started in late 1996 / early 1997 and ceased in 2000 or early 2001.
The Ref. 3917 is the basically the same model, the only difference is a sapphire glassed back to see the movement.
Does this help ?
Kind regards,
Matthias