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Nissan is a major producer of bicycles in Japan.
Pretty much all of their productive capacity goes into the manufacture of private label/contract built bicycles.
Knowing that Yama brand bicycles (or at least some of them) are/were manfactured by Nissan is a step in the detective process.
It does not tell for whom Yama badged bicycles were manufactured however.
Here is a guide regarding the reading of Nissan serial numbers:
NISSAN (Japan
YFxxxxxN based on limited size. All end with 'N', which is believed to represent Nissan Cycles, which appears on a sticker on some bicycles. The first alpha character appears to be the year with C = 1980.
Y character represents year of manufacture.
F character represnets fortnight of manufacture within that year. a letter A in that position represents the first fortnight of the year and a letter Z the last fortnight of the year.
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