The statements made about the semen have been carefully worded to say they found one match for the semen they found. They never say, or at least I have never heard it said, that only one source of semen was found.
They only say one match, they don't say one individual source. There could have been semen from 3 (or more!)separate people and that is why Nifong was so sure it was a gang rape.
No explanation has been given as to why they took those three samples from un-named people. Could it be that there was semen from 3 different guys found in her?
What three samples from three unnamed people? There's only been one other person, her boyfriend, who's been tested for a match to one sample of semen taken from her that I've heard spoken of on this forum and in the media.