I know it is not uncommon to find stamps used prior to the first day, especially in the 90's. Not my area, but came across one in a collection I purchased. This is #2560 used 8/20/91 in South Carolina. The first day ceremony was in Springfield, MA on 8/28/91.
My question is more about the cancel. Upstate, SC GMF 293 & 296. Upstate is a region in SC, not a city. Most of the zip codes in that area start 293 or 296. Guessing this is just some regional processing center? Apparently I just answered my own questions as I thought about it.