These are actors who were considered for roles in Star Trek before the actors we know were cast. This is not counting recasts where an new actor takes over an established role such as Robin Curtis taking over the role of Saavik from Kirstie Alley. However, the reboots are counted separately as they are far enough removed from the originals.
https://boingboing.net/2020/04/15/yaphet-kotto-was-almost-cast-a.html
