My understanding of passivation is a physical or chemical process to make the surface or boundary layer of a substance passive, i.e. less reactive. Aluminium does it naturally in air by forming aluminium oxide, preventing any deeper formation of oxide. So I don't know that those 'PVD' watches would be just passivation alone, as they are more cosmetic than protective. The top surface does look similar to powder coating used on e.g. suspension components. I have seen PVD Heuers where the PVD was chipped and it did look like there were two layers, so the theory of a passivation layer under a powder coating could hold true. If I remember right, though, those were base metal, which would tarnish in air - there'd be less reason to passivate stainless steel prior to powder coating.

Definitely an interesting field and worth investigation! If you don't feel it's giving away trade secrets, it would be very interesting to see the next case you do step by step.