COMEX is a French diving company founded in 1961 to explore the depths of the oceans (Compagnie Maritime d’Expertise). From 1970 to 1997 COMEX worked closely with Rolex and many of their deep sea divers were issued Rolex Sea-Dwellers as a tool to do their work. Rolex used this as a way to test some of their new watches and to resolve some with issues from COMEX such as decompression divers and their watches not being able to withstand depths. The Helium Escape Valve was deleloped and tested on 5513 and 5514 (reference for COMEX only) for COMEX before being commercially available in the original SeaDweller in 1967. COMEX watches have also been associated with records and experiments such as the max depth of 701 meters or the Hydra experiments and its common to see those watches engraved with specifics about the experiments etc.
What makes them very collectible is that they were never sold by stores and only issued to divers or officials and that they were made in extremely low quantities even after all those years with COMEX. They also have special characteristics and unique COMEX serial numbers and engravings in the casebacks which make them very interesting for collectors. The Sea-Dweller 16600 COMEX was produced between 1992 and 1997.