Is there a difference between BU259, 259, or just 59?

Here is what we learned from WGO:

Naming convention BU259G/K/GL/KL

B=Touring Coach or Class B

U=Promaster Chassis

2=200-Series

59=Wheelbase

G/K/GL/KL=model/floorplan

Dealers are using an abbreviation when they just use 259 or 59.