The third stream: instruments yes, denomination no.
The middle wing of the Stone-Campbell movement — congregations that kept the organ and the missionary agencies but refused to be organised into a denomination, and that separated from the Disciples over roughly 1926 to 1971 as the Disciples restructured. They have no headquarters, no convention that can bind, and no membership roll; what holds them together is a network of Bible colleges, mission agencies, the North American Christian Convention and the magazine Christian Standard.
Why it is filed this way
These congregations reject the word denomination more consistently than either sibling body, and there is genuinely nothing to join — no roll, no charter, no assembly with authority. What exists is a directory, a convention, a set of colleges and a magazine. Sociologically that is a denomination held together by institutions rather than by government.