Old sprite bottles question

[dr galaga]

Here's a question for any bottle collectors out there:
This past winter I picked up a case of old 10 oz. glass Sprite bottles - the kind with the embossed dots. On the bottom of all of the bottles were different National Parks, none with just cities. These came from Southern LP of Michigan.
I recently picked up an 8-pack of 16 oz. Sprite bottles (with the embossed dots) in Winona, (Southern) Minnesota. Same thing, there were only National Parks on the bottom.
I then went to my bottle collection and pulled down a 10 oz. Sprite that I think I picked up in Southern Indiana. Yep, a National Park on the bottom.
Seems kind of strange.  Did they just put National Parks on the bottom of all Sprite bottles?
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