Besides the dropouts, the stay end and stay cap treatments are not what I'd expect on an S-10-S. I'm assuming the bottle bosses were added prior to the repaint. Based on the crown, lugs and stay caps, this looks like a Finest, as opposed to a Newest. Might the cinch slot have pinched due to an undersize post? Also, if you were measuring the tube inner diameter measuring with calipers, there might have been a spec of dirt on the jaws, that could cause an undersize measurement.