User blog comment:Frodo the 9 fingered/A Third Camp?/@comment-4611874-20120812223006

Even though it is not confirmed that Annabeth was the seventh, there is a high possiblity that she is. She is one of the characters who have a POV in the MOA, but I find it unlikely for there to be another camp. Chiron said in The Lost Hero that the Greeks and Romans have indeed met, but the Gods tried their best to wipe clean those memories.