For a number of aircraft types, there are variations that you can't see just by looking at the ICAO code. One of these is the presence or lack of winglets. For the 757, these are always retrofit, and for the 737, either retrofit or in-production installation. For these types I've decided the winglet installations to be "common enough" that the possibility needs to be taken into account, and the wingspan values are therefore those with the winglets installed. If in your part of the world the winglets are such a rare thing that you'd rather have the plugin assume no winglets, you can adjust the data accordingly.
