Well yeah, Mississippi isn't that far away. And all they got is all the gravel from everywhere else.
Talk about it all runs down hill!
That publication is very informative and a great visual identification reference.
I knew the Sioux quartzite is found along the rivers in Arkansas and Mississippi,
I don't know why I didn't think more about everything else ending up down there too.
I did notice when first looking at your pics how some definitely looked like "Crowleys Ridge" agates
but didn't get into that because that type of agate can be found in many places.
And in your above mentioned reference it's interesting that they call similar agates,
Plate 2, Page 5, #'s 10-13, "common" agate types and not Crowleys.
Anyway, it's obviously worth the hunt.
Don't give up on looking at any stream channel alluvial deposit mining operations closer to home.
Good luck.