1521

The same case under two brand names is normal here, not suspicious

Von Büren supplied dive cases to other manufacturers, so the case on a period Blancpain, Doxa or Heuer diver may be the same construction as a Squale. Case commonality across brands is the expected condition for this era and treating it as evidence of a marriage would produce false findings across several manufacturers simultaneously. What matters is whether the case, dial, movement and caseback belong to the SAME watch, not whether the case design appears elsewhere.

The asymmetry is machined and is the thing to verify

The straight-cut section of the case wall appears on the crown side only, and the crown sits at four rather than three. That combination has to be cut into the case and is not something a copy adds cosmetically. Look at the case from directly above and from the crown side: the asymmetry should be unmistakable and clean.

Military provenance on this case belongs to another brand

The 1521 case's documented navy issue history attaches to Blancpain-branded watches, not to Squale-branded ones. A Squale offered with an implied military history through the case reference is conflating two different things, and the distinction matters commercially.