They didn't miss it. Remember, nobody was under arrest at that point. Nifong only had a duty to inform the defense that their clients were excluded, and furnish them with any portions of the SBI report addressing those clients, NOT the alleged victim. They didn't have a sample of the boyfriend because Mangum didn't tell the SANE nurse about having sex with him during the five days prior to the alleged incident, which she was supposed to do because alleged rape victims are asked this question, and it's a very important question. Mangum clearly lied to the SANE nurse and, more importantly, Nifong knew that she had lied to the SANE nurse, thus impeaching her entire statement to the entire event, when he went into the GJ to seek his indictments.
According to that article in the N & O, they did miss it.