Since you're in Spain I would try contacting Honda corporate. I was able to establish the year of manufacture, generally, because on the wire harness loom, by the middle of it under the gas tank on the C110 50 cc motorcycle model, is a date ribbon attached to the wire harness/loom. Look for it, it's a white label with the date of manufacture by-year on it. I'm not-sure exactly where that would be on a step-through, I expect it would be somewhere where a body panel or another piece concealed it.
With the steering head serial number/VIN, and that wire harness/loom date, I submitted a request to Honda of N. America for a confirmation letter of the date of manufacture. They sent me back a letterhead stating that the number and the date were consistent with a motorcycle manufactured and sold in the USA between two years on either side.
You could also examine inside any body panels or elsewhere for a foil decal with "this motorcycle conforms to requirements for the USA on date of manufacture," or something similar. On newer bikes, it's usually by the steering head.
