the three letter code of an airline is ICAO - DLH
the two letter code of an airline is IATA - LH
-xxx stands for Cayman islands I think and is the Reg for the country where the plane is registered, as your car should have NL
. The Country doesn't have to do anything with the letter code of the airline. Every two letter code airline has even a three letter code but not every three letter airline has a two letter code also. VP
-xxx is mostly used to cut txws for airlines or companies. All Aeroflot western built planes are registered VP
Hope that helped you and wasn't too confusing.