Actually, it seems like the shopkeepers all tend to have either items that we already have or items that will be released in the future. Like with the Ring Belts. I'm pretty sure we didn't have 'em when Nicolette first appeared wearing them, but we have 'em now.
And there's the Classy Brown Skirt that Elizabeth wears, and Penny's White Flats, and Kamea's blue version of the Candy T Shirt, and so on.
So, who knows. Maybe eventually we will have all these cool skirts and whatnot.