No possibility. The S20 was made from 82 to 85.
The 430 was made from 1997 to 2012. The serial number structure won't indicate the year. Some features, like which engine it has, what decals, whether it has a ROPs, will indicate older or later. You should be able to get in touch with a dealership and they call look up the serial.
Congratulations! Steiners are really cool machines. I've wanted one since I was a teenager, and just got my first (an 85 S20).