GTs58
I'm the Wiz, and nobody beats me!
The Schwinn bars were unmarked until 1965-6. As far as I know there are no other parts on these 50's bikes that are stamped to indicate what the actual year these were built. It's not that unusual for a Schwinn to be built 5 or 6 months after the serial number was stamped on the component. There was a late 70's or early 80's Schwinn posted here recently that had an 8 month lapse between the serial date and the head badge date.