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Made in Taiwan.
First letter indicates Giant factory code. Second and third digits in the serial indicate production month. XX in the example above (05 to 12 - May to Dec). YY in the example above (01 to 04 - Jan to April). Fourth and fifth digits indicate year of production. 84 or 85.
Bikes made in Taiwan usually had around an 8 month production and shipping timeline before they were sold in bike shops around the world. In May of any year, factories would usually switch production to making models for the following year.