It's more complicated than that. For example company A may design a reg and then farm it out for production to company B. Company B may then make similar models under license and sell them through company C.
The Scubapro Mk 16 S55 is a good example. The Mk 16 and S555 were both Scubapro designs that Tabata was contracted to produce. However, Tabata also made and continues to make licensed versions that were sold by TUSA (as in Tabata USA) as the RS-460 - a combination of the R-400 first stage and S-60 second stage - both of which are dead ringers for the Mk 16 and S555 with the exception of some minor cosmetic changes. And the current R-400 also includes the same poppet upgrade that the Mk 16 got a year or two ago when the new Mk 17 poppet was retrofitted to the Mk 16.
It is a good arrangement for Scubapro as they have no need to devote the resources to manufacturing resources for what is a small volume item, so they save money and benefit from Tabata's world class manufacturing facilities. Scubapro also saves on production costs by cutting a deal to allow Tabata to sell licenced copies and Tabata benefits from access to the Scubapro design that they then market through TUSA.
Where it gets confusing is that Tabata is a Japanese company with production facilities in Japan and Taiwan, but the Scubapro box the reg comes in will suggest the reg is made in Italy. I am not sure if just the box is made in Italy or if the parts are shipped to Italy and assembled there. I suspect the latter.
In any event, Tabata has been making scuba equipment since 1952.
Sherwood is another early maker of regs. They were around for 30 years making medical and gas handling equipment before getting into the scuba manufacturing business in 1955, but even though they made regs or parts for nearly every company selling scuba regulators, they did not sell a reg under their own name until 1972.
Beuchat is a third early maker of scuba equipment and early Scubapro and Beuchat models have the same similarities as do Scubapro and TUSA.
Between the three of them, I suspect they make the majority of regulators sold worldwide.
