Random,
If you're only flying domestic you didn't have to get the SIC type. At least not per FAA regs. It was created to allow you to show foreign CAAs you have been trained on the aircraft. An FAA Inspector knows if you are sitting right seat in Brand A Airlines airplane, you have been trained by Brand A as an F/O. Sort of like adding "English Proficient." Since being proficient in English was a requirement to hold a pilot certificate, if you held a pilot certificate an inspector had made the determination you were proficient in English. But ICAO won't follow that logic.