each airline is designated a number code by the a/c manufacturer, and the dash number after the aircraft type is that code. dont know why they do it, but must be a way of keeping track of the aircraft throughout its life...
eg. qantas i think is -12, so all qf 737's, 767's 747's, as long as they purchased them new, will end in -12, with tthe number in from of the 12 being the model number... hope i havn't confused u...
