[Spoiler] Brain scan question.

[cantremember]

Interestingly enough, I think the game plays from a third-person point of view of all the characters. You play as multiple people, but specifically follow the journey of the different Simons and their experiences.

Yes I see it this way too, that or either partly as a flashback.
Because imo, the very fact that you walk around and are able to choose actions as Simon-1, means you are him and would inevitably just live on in Toronto after the scan. So either the game switches "perspective", or Simon-1 and 2 can be considered like flashbacks. Since the things you did as Simon 1 & 2 are things Simon-3 physically never did, they're only mere memories to him once he starts existing.