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Made in Taiwan.
The first two numbers in the serial indicates year of production. 89 = 1989, 90 = 1990. The third and fourth numbers (as shown in the examples above) indicate production Month. XX = 05 to 12 May to Dec. YY = 01 to 04 Jan to April. For all serial number sequence explanations, see the mid-school serial guide page.
Mid School Serial Guide
Bikes made in Taiwan usually had an 6-9 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.