Appliage: Building a Serial Number Decoder for Appliance Age Lookup

I have been building Appliage, a free appliance age finder based on serial numbers. The interesting part is not the form. It is the date logic behind it. A lot of appliance brands use short year codes. GE, for example, reuses year letters. Other brands use year digits that come back every ten years. If you only look at the serial number, one input...