I live in NC also and while I don’t know the legal answer to your question, I would just send it what is easy. It is not something they scrutinize. If it is easy to send your marriage certificate, I’d go ahead and do it. But if you can’t place your hands on it, I wouldn’t worry about it – they will let you know if they need it but I’d be very surprised to hear they want it. Remember, the majority of homeschoolers have a different last name than the one they graduated high school with. If it were a concern of theirs, they would say to send the marriage certificate right in the directions.