Think of it this way, in these big factories in Japan. there was an area that built frames and were serialized when they were built, then they sit in a warehouse for awhile until they are needed to build bikes, they are painted and decals. then built up. So although the SN says 83 the bike was built as 1984 model.

the one in the pic above was probably a early 1983 model that had the holes drilled in the headtube for the badge, most likely a mid to late 1982 built frame that at the time required the holes for headbadge.