Bodak...
Individual Vehicle Armor Comes in Ratings (Rating 1-20)
Personal Vehicle Armor Comes in Ratings (Rating 1-10)
A Rigger Cocoon has no ratings, even though it has Armor 20.
Worn Armor DOES NOT COME IN RATINGS. They have an Intrinsic Armor Rating, but that is not the same thing, and is not limited at character Creation. I could purchase Military Grade Armor if I wanted to do so (and spent the Restricted Gear Quality) because Personal Armor is not Rated...
You are talking about Apples and Oranges. Your line of reasoning would eliminate most trucks, some cars and even a Motorcycle , some low end security vehicles, and even some drones from being purchased, even though they fall well within Availability limits. You do not include Non-Rated equipment in the Ratings above 6 limitation.
Not even sure where you got that idea from...