Some points about Star Trek VI:The Undiscovered Country

[Henoch]

How would it work, the shuttle mission being Spock's "first command"? We'd both have to narrow down the definition and make assumptions about Spock. But both are certainly doable.

Having a "Command" and being in temporary command on a ship or a landing party are two different things.
To get a "Command", a Command-level Officer of at least Captain (Kirk) assigns a ship (shuttlecraft) and crew (six other personnel) to an officer (Spock) for independent action (in this case, explore the nebula) away from the command authority (Kirk on the Enterprise). That officer (Spock) is solely responsible for the ship, crew, and success of the mission.
In contrast, Spock being in temporary command of the Enterprise while Captain Kirk is on a planet or another ship is not a Command. The Enterprise was not assigned to him by a Command-level Officer. The highest ranking officer can take Command of a ship if he (and the command crew) of the ship can officially prove that the Captain is dead or unable to continue command of the ship (comma, insane, too old, etc.).
Technically, Spock was in fake-Command of the Enterprise in The Menagerie when he faked Kirk's orders that Spock was in Command. This Command came first if you use Broadcast Order, but second if you use Production Order, but in that case, it was fake so it shouldn't count. Up until that point, we don't see Spock with a Command until The Galileo Seven.

 

[Timo]

Indeed, nothing in TOS (or DSC and the related shorts) so far actually contradicts the idea that the shuttle sortie would have been Spock's first command. We never see him in charge of landing parties in the preceding adventures, say. It's the unseen we have to mind, which is where the narrowing down of the definition, perhaps beyond that of the real world, comes to play.

Say, Spock is the ranking officer in the landing party when Pike disappears, and commands the actions before returning to the ship, but we can dismiss that on so many grounds. Any other, "proper" planetside action in his career should count, though. How do we "protect" Spock from those, for several decades straight? In DSC, Pike surrounds himself with relatively high-ranking officers, so Science Lieutenant Spock might indeed get few opportunities to command any away action under Pike. Is he even the Chief Science Officer, or just one of the juniors? Pike's previous one left the ship at Captain rank...

Timo Saloniemi

 

[BK613]

Even on a landing party, the command structure is there, just a communicator call away (if the starship is there), but during the Galileo mission, Spock is the senior officer present in a situation where there is no phone-a-CO option. Hence his first situation where the authority, accountability and responsibility are his alone.