When the Session manager starts a session, they specify what movie files you'll be watching in that session.
You need to load these files before the session can begin.
So... when searching for these files, you only need to specify the folder they are in, and Syncarella will find them by name.
And yes, Syncarella can tell if the file is the correct version because it does a hash test of each file when the Session manager selects it. It sends the hash to all the users and uses it to determine if you've selected the correct file.
In other words, you can't select the wrong file.