Curious how much collaboration between writers/producers and actors would be happening at that early stage. To my eye and ear the early season one takes on the characters were very much on the page and writer driven. Later I think Shatner and Nimoy began influcing the shape of their characters. OTOH McCoy seems to be written for Kelley.If the timing is correct, pull isn't necessarily required. Could be as simple as the writer (Roddenberry?) asking for suggestions.