Simpson L/E Brush ?'s

I have to ask the Brush aficionados in this house!...especially Simpsons. Simpson offers their standard line of handles and specific badger grades, they also have limited edition brushes for sale too as many know...Many times I see brushes that Simpson calls L/E like a "Duke 2 in Best w/faux ivory turned handle", or "Chubby 1 Super w/faux ivory". I could swear that these style handles and badger grades are regular stock? Does anybody know what the difference is? Or is it just about availability? Thanks Everyone!
-BB