This concurrency, of course, runs along the Oklahoma-Arkansas line, though it does swerve fully into each state toward the north end. The OK-AR-MO tripoint marker is just to the west of the road, for instance.
The first assurance shield northbound currently shows OK-20 alone, although it looks like southbound OK-20/AR-43 is shown.
At one point it was signed OK-20/MO-43 going northbound, which was never actually correct, since the concurrent stretch of highway doesn't actually enter Missouri. (Once it reaches MO, both OK-20 and AR-43 ends and the road becomes solely MO-43.)