SUB 300T Conquistador

The valve is a physical fitting and can be verified as one

A helium escape valve is a sprung one-way fitting through the case wall, usually on the flank at nine o'clock. It has a distinct external component and a mechanism behind it. Counterfeits and lesser homages sometimes reproduce a valve-shaped protrusion with nothing behind it, or a decorative disc. Establish that the fitting is real before treating it as evidence of the reference.

First COMMERCIALLY AVAILABLE, not first outright — and the distinction is the whole claim

Doxa's priority claim is correct with its qualifier attached and misleading without it. Rolex filed the patent — Swiss CH 492 246, 6 November 1967, granted 15 June 1970 — and fitted a valve to the Sea-Dweller from 1967, but supplied those watches to commercial diving contractors such as COMEX rather than selling them to the public. The 1969 SUB 300T Conquistador was the first such watch anyone could buy. Neither firm originated the idea: it came from Robert A. Barth, a US Navy saturation diver from the SEALAB programme, who brought the one-way-valve concept to Rolex. State the distinction in a report rather than repeating either brand's unqualified version.