From what I've been able to tell "flavor range" is just that---the "flavor" juices that they have. Mostly, they are simple. Pineapple, apple, banana. These are available in any ration of PG/VG that you want.
Specialty juices are juices that have been "designed" by the people at FSUSA. These are an unknown combination of flavors (they don't share the recipes). They are developed at 50/50 PG/VG and aren't available in any other mixture. This is because whoever tests them finds that this is the optimum taste for what they are shooting for. In other words, if someone would try to mix a specialty flavor in 100% PG, the tastes would be "off".