Richard,
Other forum members know a lot more, but I think that here Kb is short for Kampfbeobachter (observer) while Vorschule Stolp/Reitz refers to the training school at the airfield with the same name.
A link with lots of details, although in German, here:
http://www.kunefke.de/index.php/luft...tolp-west.html
Regards,
Leendert