Yours DOES seem to be all-original, at least compared to the pic in the 1974 catalog (by which time they did change the model name to "Competition") even the pump and shorty half-fenders look original, as well as the padded springer saddle.
The "men's" frame was a bit different, and they still called it "Nishiki Semi-Pro" for a few years before 1974 cause I once owned one, the lugs were a long-point style, kind of a copy of a BCM Pro lug, rather than these ornate ones on the lady's frame (which were also used on some Azuki frames, same importer in the US).
Check out the Nishiki catalog scan on Velobase:
VeloBase.com - Catalog Scans