Does anybody know the distinct difference(s) between p/n 52596-09A ($219 list price) which is an adjustable rider backrest mounting kit for '09-later touring models and p/n 52546-09A ($109 list price) for '97-later Touring and Trike models and p/n 52593-09A (list price $219) for '97-'08 Touring models?

What is the actual difference that prevents one from installing 52596 on a 2008 model...and why the substantial price difference compared to 52546?