::::::::Your citation for 豆田 = "Mameda" illustrates the problem. You merely provided a link to the Japanese "Wikipedia" page that describes Mameda town - today. You did not establish that this reading was used 1.) locally, 2.) at the time when the tramway operated, and 3.) by the tramway operator. It was not uncommon to find localities - and businesses - which used "local" pronunciations ("readings") of place names. This practice has faded, but has by no means disappeared: in virtual defiance of Tokyo-based authorities, Kyoto clings to "Kyoto-ben" pronunciations of certain well-known place names. Thus: 豆田 might well have been "Mameda." It might also have been "Mameta." This being a Kyushu place name, it might also have been "Mameden;" "Zuden" and "Tōden" are, as is said, "unlikely but not 'impossible'."