Attached is a "Service Letter" from M-B explaining their practice regarding "years." M-B issued similar letters prior to and after this 1961 example. Please remember, if ordering parts or trying to tie down mechanical or trim details, it is the chassis, engine or body number that remains paramount regardless of what "year" may have been assigned to the car for sale purposes.
Since the car in question was built and delivered in the same year, there is no reason that any state would register it as one year "newer." This was an internal M-B policy only and designed to spur sales of leftover vehicles. In any event, what benefit would one today (54 years later) be seeking to have a car registered with a different year from when it was built.