1. Read what is physically present
Photograph the caseback and record every character before drawing a conclusion. The case reference, serial string, manufacturer marks and later engraving are separate observations.
2. Identify the system actually used
For many Seiko watches of certain eras, the first serial digit may indicate a year within a decade and the next a month, with codes varying by manufacturing period. This does not, by itself, establish the decade. Confirm the actual maker and caliber before attempting interpretation.
3. Cross-check the candidate date
Movement introduction and retirement, signed dial code, case code, catalog photography, bracelet configuration and period advertising can collectively narrow the production window. Replacement components can make contradictory evidence entirely unsurprising.
4. Record confidence
Use “confirmed,” “likely,” or “tentative,” followed by a citation. Explain a remaining contradiction rather than deleting it.