A beaker full of death wrote:
Seems in one iteration King knew she was fourth in command. Wasn't that fanon that evolved years later?
I don't have it in-hand, but I believe the Writer's Guide circa the second or third seasons state that she's fourth in command after Scotty. I suspect this was inserted by Roddenberry as a nod to his mistress bugging him about her crappy part. It was an easy thing to claim yet never act on. How frequently did they even need to go further down the chain than Scotty, after all?
It may not be in the Writer's Guide, my memory is hazy. I believe that it appears in some early semi-official material -- The Making Of Star Trek
, The World of Star Trek
or The Trouble With Tribbles
(the book, not the episode) is where I'd look.
Nichols has repeated that Uhura was 4th in command since forever. It wouldn't shock me if that particular tidbit worked its way into the story at some point. It would shock me a lot of MLK actually knew it -- only the most zealous fans even cared.