Excerpts of the President's News Conference
Here is an inquiry relative to the use that might be made of questions that are submitted to me and which I do not discuss. I had supposed that the rule about that was that questions that were submitted and not discussed would not be discussed in the press. I don't mean by that that it isn't perfectly proper of course to discuss the substance of the questions, but I did understand that it was the rule that if a question were submitted to me and was not discussed by me that no report was to be made, one way or the other, about the fact of the submission of the question.
Source: "The Talkative President: The Off-the-Record Press Conferences of Calvin Coolidge". eds. Howard H. Quint & Robert H. Ferrell. The University Massachusetts Press. 1964.
Calvin Coolidge, Excerpts of the President's News Conference Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/349188