Coming from the wacky world of marketing, ‘brand’ is not a perfect basis for a taxonomy for derailleurs - but it is probably the best available.
A typical problem is whether a Raleigh branded SunTour VGT luxe is properly listed under ‘Raleigh’ or under ‘SunTour’. I have copped out and listed it under both.
A mind bending test of any taxonomy is the takeover of Huret by Sachs in 1981. In some cases the same design was branded, in chronological order: ‘Huret’, ‘Sachs-Huret’ and possibly finally ‘Sachs’. Before the takeover of Huret, Sachs itself had branded its own products ‘Fichtel und Sachs’ and then ‘Sachs’, and after the takeover may have produced some of its own designs under the ‘Sachs-Huret’ brand. Finally, before the second world war, Fichtel und Sachs had factories in parts of Germany that ended up in West Germany and other factories that ended up in East Germany as part of what was a different company. I can see no perfect, clean way through all this - so you may have to search around in the site! In general I have tried to list Sachs-Huret designs under both Sachs-Huret and then either of ‘Sachs’ or ‘Huret’ depending on where I consider that the design originated.
Another difficulty can arise when it is unclear what the brand name actually is, particularly when the product originated in a country that does not use the Roman alphabet. For example SunTour famously appears on 1950’s and 1960’s designs as SunTour, Sun Tour and Suntour, presumably because this kind of detail was not that important in the Japanese home market at the time. For similar reasons early Shimano gears did not have the word Shimano on them but were prominently labelled ‘3.3.3.’. Finally Kharkov derailleurs, produced in Kharkiv in the Ukraine (part of the USSR at the time) were not branded using the Roman alphabet at all, they were branded using the Cyrillic alphabet. The company name is probably best romanised as ‘Kharkov Velocipyed Zavod’ and the derailleurs often have three characters on them, so they are sometimes called ‘KVZ’. However the Cyrillic characters look like ‘XB3’ so this is sometimes identified as the brand. There are also plenty of ways of romanising the word ‘Kharkov’, Arnfried Schmitz refers to it as ‘Charkow’. Some Russians seem to refer to the company a ‘HVZ’, implying a spelling of Kharkov that starts with an ‘H’. I have unilaterally decided the brand is ‘Kharkov’!
Despite all this, I hope you find what you are looking for.