Baby weight around seven month birth

Patient: My ex girlfriend now tells me she had my baby. We had sex on May 18th so 9 months would be February 18th. She gave birth on December 6th and the baby weighed 6 pounds 9 ounces. Is this possible? All the research I do say the baby would be 29 weeks and around 3 and a half pounds at most. SO is this possible that the baby weigh so much?