” I think you are definitely correct about the meaning of “interdenominational,” and about the error of using it to designate organizations that are not intentionally facilitating a particular form of cooperation between denominations.To be genuinely interdenominational, I think that the board of an organization must include members appointed by and responsible to the denominations whom the organization intends to serve.In Christianity the qualification ecumenical is originally (and still) used in terms such as "ecumenical council" and "Ecumenical Patriarch" in the meaning of pertaining to the totality of the larger Church (such as the Catholic Church or the Orthodox Church) rather than being restricted to one of its constituent local churches or dioceses.
Ecumenism and nondenominational or postdenominational movements are not necessarily the same thing.
For some reason I expect my recommendation on the usage of nondenominational and interdenominational to be heeded about as heartily as my advice to my kids. And I wish authors and editors would be more selective in their use of the terms.
And as Andy Le Peau commented on reading this blog, “If an editor can’t be curmudgeonly, what’s the value in being an editor?
You need to be able to sign wholeheartedly our doctrinal statement, support our values and mission, etc.
Whether this puts you at odds with your own denominational affiliation is between you and your own denomination.