Third time I've watched it and
while I love the movie the anachronisms drive me batshit crazy.
Rubik's Cube & Walkman weren't available yet 79. The Shuttle main fuel tank wasn't brown until '82.
I-675 didn't exist at the time nor did the 35 bypass around Xenia, 35 was also still a two lane surface road between Xenia & I-71. Finally the four lane extension of 35 W of Dayton towards Drexel did not exist (part of the white man's plot to keep a brother down) .
I'll just swallow the part about the flatlands west of Dayton becoming Appalachia (if nothing else I can just pretend it's a 10-15 miles farther south where the land does get a bit more rolling) although I imagine residents of New Lebanon might be a bit annoyed.