Speculation. We'll see what the writers decided. The 63's disappeared either through supernatural means, or conventional means. I'm figuring conventional, such as knockout gas; it would explain all those unlocked doors.
I don't know how Sylvane got placed where he was found. Maybe from the night before so he simply woke up.
Why hasn't he aged? Maybe was in suspended animation? It seems likely he was "programmed" for a mission at Present Day though.
First two episodes raised a lot of questions. Let's see what happens, even if it is a Crook of the Week format.