日商工は３団体でも一番歴史が古く１９２２年に発足した。
(As backdrop, the 経済連、経済交友会 and 日商工 are the three largest business lobbying organizations in Japan according to the Manga. And 日商工 is the oldest.)
My question: what does でも mean here? でも usually have three meanings:- 1) but 2) even including and 3) among other things. But でも here does not seem to fit in any of the above meanings.
Whether the で and the も are analyzed separately or as one unit, でも in this sentence would emphasize the subject as the superlative case among the three, loosely fitting within the second usage you listed ("even including").
Sometimes it's hard to find a corresponding usage category in a J-E dictionary, which usually list only the main usages, whereas in a more comprehensive J-J dictionary you can find a closer match.
