I can't find any National Road signs in downtown Columbus OH;
https://gis3.dot.state.oh.us/ScenicByways/HNR.html shows it using either Grant or Drexel, not 3rd/4th.
https://www.franklincountyengineer.org/wp-content/uploads/PDF/TravelersGuide.pdf (p. 26) says the National Road originally used High and later moved to Drexel, giving Drexel as the route to follow now.
Bridgeville Drive west of NorwichUS 40 west of Cambridge, NOT Manila Road (but Fairdale Road
is signed)
Peacock Road west of Old Washington has a small
OLD NATIONAL ROAD TOUR sign (posted by Guernsey County).
This tour sign points right, implying it loops east to use Old National Road thru Old Washington - and
this is a bigger sign confirming it.
There's another tour sign on
Bridgewater Road west of SR 513, but I don't see any east of SR 513. Perhaps this should be a gap, since half of our route was never the National Road. Or take it on I-70 like
https://gis3.dot.state.oh.us/ScenicByways/HNR.html shows, but there doesn't seem to be any signage to the east to and along SR 800 either. So have a gap until I-70 exit 204?