When Spock first meets Trelane at the bar, he said he didn’t know there was a Vulcan bartender on board. Later, as the wedding planner, Trelane looks at his reflection and is clearly Andorian. I think we as the audience see him as Trelane, but Spock and the rest of the crew never see the “real” him. This would explain why Spock doesn’t remember him in TOS.