Right next to Mitchell in “Where No Man Has Gone Before,” was Lee Kelso. In some ways, this dude was destined to become one of Trek’s very first “red shirt” even though he was sporting a kind of off-salmon tunic. Be that as it may, Lee seems very familiar with the Enterprise in “Where No Man Has Gone Before,” which means it’s truly possible he’s already on the Enterprise in the Discovery episodes.
This is a huge one. In the Discovery episode, “An Obol For Charon,” Pike says that the Enterprise has a chief engineer named Louvier. In the same episode, Pike says “I don’t feel the Enterprise will ever have a chief engineer more in love with his ship.” Clearly, this is a foreshadowing joke about Scotty, who will always love the Enterprise way more than whoever this Louvier dude is.
As Discovery has shown, it’s not unusual for a starship to have more than one engineer. This means Scotty could be a junior engineer on the Enterprise at this point in time, working under Louvier and loving the Enterprise.
Oddly at this point in time, Scotty could also be serving aboard the USS Discovery. Why? Believe it or not, we’ve never truly seen the chief engineer of the Discovery. Stamets is an engineer, but he isn’t the chief engineer. Reno is an assistant engineer. In the second season of Discovery, there has been passing references to “the chief engineer,” but we’ve never really seen this person.
Moreover, in the first season of Discovery, in the episode, “Despite Yourself,” Captain Lorca pretends to be the chief engineer of the Discovery, by doing an impression of Scotty! If Mirror Lorca knows about Scotty, it seems highly likely Scotty is around, either on the Enterprise or close by on the Discovery.