The three monitor's in Cranbrook drive. Each has a different kind of personality.
First monitor: Happy, playful.
Caught in the first monitor and Caught in the flashback are wearing the same clothes.
So my idea is that First Monitor Caught (referred to from here as FMC) is who Caught was to begin with, he is the "real" Caught.
SMC is what prolonged exposure to Slendy has turned Caught into. I'd say it turned him insane or perhaps there was Slendy possession. And that SMC became Showtime.
TMC is Caught as he is now, somebody (I'm guessing Roivas) found some way of separating Caught from Slendy, or getting Slendy out of Caught or burying the Showtime personality or SOMETHING like that, which also erased Caught's memory.
The renewed Slender exposure is bringing SMC back to the fore and if the latest video is anything to go by it looks like SMC might be the only one left.