For a dual line kite...
Top wind range- when the wingtips start to shudder & shake, it's time to land & put the kite away before it gets broken.
Bottom wind range- if you can't get the kite to fly, that's beneath the kite's wind range. Some pilots will be able to get it to fly, some won't. Bottom wind range isn't so dependant on the kite, more the pilot. I've heard of people that can get a vented kite to fly indoors...
Hope this helps, like the others said above, take the advertised wind ranges lightly. They're meant to give you an idea before you take the kite out of the bag, or before you buy it.