Re: Why didn't Chekov ever make Captain?
. . .Assuming Sybok is a Vulcan of some intelligence, why wouldn't he notice that Chekov ISN'T WEARING a captain's rank insignia?
Sybok isn't in Starfleet, he's a civilian. I'm a civilian too, and I would never be able to distinguish American naval rank insignia, but I would be able to for army and perhaps air force, at least for commissioned officers. I'd have less luck with rank insignia of other countries.
Dr. Howard, Dr. Fine, Dr. Howard: For duty and humanity! --Men in Black (1934)