I just noticed something not sure this a K4 thing but went to archive items and there is an option. "add other device collections" When I choose it showed my other Kindle and K4PC as options. I could add the collections from my K3 to it. This would of been nice last night if I had bee awake enough instead of having to manually remake my collections.
Ah I see it's was introduced when you own a second Kindle or have Kindle For PC installed.