Actualy INNFlight from what I heard you can only take the DLR once but for each airline. For example you go there for Lufthansa Italy and if you fail you cannot apply for that one again, but if you want to apply to GermanWings, TurkishAirline or some other you still can. Of course you have to go and try to pass the DLR that time. Which is not an easy thing to do.
I'm not absolute certain about this of course, but I think this is it.