Normal. I would, absolutely, start preparing for a combo interview. Make sure your spouse attends also. In our case, my wife was informed only 2 days prior to her N-400 interview that it would be a combination. Some people are not notified until they show up. For the I-751 part of the interview, our officer wanted to see evidence of a bona fide marriage from date of original I-751 submission until day of interview. That included driver licenses, leases, bank statements, etc. He also wanted to see any travel documents (ADIT stamps) my wife used. Good luck.