The "SC" in the model stands for Self-Propelled Commercial.
It's the commercial-duty version of the mower that you have (but it is self-propelled with a 5-speed gearbox). The primary and most visually-obvious difference is all-steel wheels with sealed bearings. The motor also will have an oil pump and external spin-on oil filter, and there may also be deck guards (AKA rub strips) on the sides of the deck. Most of the other parts are identical to the consumer-grade version.
They are fairly rare and desirable by those that understand what they are. If it is in good condition and you can get it for a reasonable price, I'd go for it. There is a lot of info on the commercial models on the mytractor site in the walk-behind forum. If it has a damaged deck, you can switch all of the other parts over to your deck to make it into a 14SC.