Why didn't Spock mind-meld with injured Captain Pike in "The Menagerie"?
Mendez shows frustration that Pike can't reach out, no one can reach in, and that his mind is working normally.
In terms of production numbers, "Dagger of the Mind" was apparently filmed about 4 or 5 episodes before the "Menagerie" framing story, and originally aired 2 weeks earlier.
So it had been previously established that Spock had this ability.
Was it unmentioned only because they were uncertain of actual airdates in those days?