Daryl, Although it was not common, some veterans did have multiple army serial numbers assigned but not at the same time. For instance, an enlisted man undergoing flight training would be assigned an enlisted ASN such as 35137895 until he completed his training. Upon completion, he was commissioned as an officer at which time his enlisted ASN was no longer used and he was assigned an officers ASN as Ellis H. mentioned such as O-134789. The other branches were similar, in that your relative was assigned his original (Which would still be listed within NARA), and when he was later commissioned it was changed to reflect his officer status, which appears on his certificate of service. If your father was selected for military college programs for the medical corps, he was commissioned after he graduated. If his records were lost in the fire of 1973 and NARA provided you with a certificate of service, it is most likely that his enlisted records were lost in the fire and the only proof of his service they can provide is a validation from sources that only reflect his service after his commission, which explains the new officer ASN. Rick