Because he did not have a working device, Gray filed a caveat or preliminary disclosure instead of a full application, and he was not especially concerned if some details of the apparatus were left somewhat vague. But as we have seen, Gray's mental model was the lover's telegraph, which did not require multiple diaphragms. So it is not clear why Gray still thought he might have needed multiple diaphragms to transmit speech. Similarly, an inventor may simultaneously consider alternate mental models which contradict one another in important respects. Gray's caveat is largely consistent with a mental model for the transmission of speech based on the lover's telegraph, but his remark about multiple transmitters is more consistent with a mental model derived from his musical telegraph experiences, where composite tones were produced by combining single-tone transmitters.
Mental models are provocatively incomplete, often fuzzy in important details.