I happened to be on the road early this morning, when I discovered the TOS ep "The Omega Glory" on TV Land on a publicly available TV at a stop I made. Apparently, TV Land is playing UN-remastered TOS with the roosters. 
When I had a chance to use my computer, I visited the Memory Alpha article on "The Omega Glory", then visited the article on the Exeter's Capt. Ron Tracey:
http://www.memory-alpha.org/en/wiki/Ronald_Tracey
One passage in the article really caught my eye:
This passage surprised me. Apparently, the authors were not considering Captains Krasnovsky and Chandra from "Court Martial" to be currently serving captains of starships. I'm not sure if this is an oversight or if their captaincies could be of vessels lesser than "starships" (presumably starships-of-the-line, such as the Constitution-class) or if they are awaiting appointments to starship commands, possibly with a promotion as well.
Could it possibly be that starship captaincies in the TOS era are usually reserved for flag officers, and that Kirk, as a "mere" captain, was on the fast track to Commodore as well? Could it be that Constitution-class vessels are usually commanded by Commodores or Admirals, and that Captains in this position are rare? If so, would the represent another discontinuity with ENT, or not?
One thing TOS did not really show are lesser classes of starships. Could it be that Starfleet of this era used Commanders and/or Captains most commonly for these unseen ships?
Or is Memory Alpha's article on Captain Tracey off the mark here?

When I had a chance to use my computer, I visited the Memory Alpha article on "The Omega Glory", then visited the article on the Exeter's Capt. Ron Tracey:
http://www.memory-alpha.org/en/wiki/Ronald_Tracey
One passage in the article really caught my eye:
Tracey is the only Original Series character, other than James Kirk, to wear a Captain's rank insignia and be seen as the Commanding Officer of a starship. All other active starship commanders were commodores (Matthew Decker, Robert Wesley, and Commodore Stocker albeit temporarily).
This passage surprised me. Apparently, the authors were not considering Captains Krasnovsky and Chandra from "Court Martial" to be currently serving captains of starships. I'm not sure if this is an oversight or if their captaincies could be of vessels lesser than "starships" (presumably starships-of-the-line, such as the Constitution-class) or if they are awaiting appointments to starship commands, possibly with a promotion as well.
Could it possibly be that starship captaincies in the TOS era are usually reserved for flag officers, and that Kirk, as a "mere" captain, was on the fast track to Commodore as well? Could it be that Constitution-class vessels are usually commanded by Commodores or Admirals, and that Captains in this position are rare? If so, would the represent another discontinuity with ENT, or not?
One thing TOS did not really show are lesser classes of starships. Could it be that Starfleet of this era used Commanders and/or Captains most commonly for these unseen ships?
Or is Memory Alpha's article on Captain Tracey off the mark here?