McCoy spent a few months on the planet Capella IV ('Friday's Child'). Judging from the uniform he's wearing in the screencap
, this must've been what he was doing immediately before joining (or rejoining, depending which writer you believe) the Enterprise
crew in between 'Where No Man Has Gone Before' and 'The Corbomite Manuever.' Terrell was Kirk's age (32 in 2265*), and serving as first officer of the scout ship Sagittarius
starting around that time period (The ship is 'nearly new' in Vanguard: Harbinger
). If the other elements of his backstory via Memory Beta
(specifically the part about Derus VI) are to be believed, seems he'd be a natural to accompany McCoy for a few months on a Federation goodwill tour of Capella while recovering from his ordeal on Derus, before getting the XO gig on the Sagittarius
* He would have already graduated from the Academy by the time McCoy signed up, assuming McCoy-prime went in the same time Abramsverse McCoy did.