First - no, you need only ONE log, since all x,y,and z is stored there...
So if you can retreive the LOG for one named user, you should be able to play it back to him...
And Second, if a log for any named user exists on you server, you should be able to load this. maybe you want to generate a second CSV file, that hold all usernames that have been saved, so you can generate a pick list
Sorry, I am also working on the rotary challenge ;-)