This number could point to two possibilities: First, it is like the one on my '83 Paramount, i.e. G=July, 83=1983, and 8628=the # frame built in July 1983.

Since Paramount/Waterford never built that many frames in a year, let alone that many in one month, the second possibility is more likely. G=Giant, 83862=Serial number, and 8=1988. Thus this might be a higher end Giant built Schwinn, repainted and Team Paramount decals applied.

I've asked the seller where the serial number is located.