During the course of season three, we learn that Rumplestiltskin has run across Peter Pan before, when
Pan tried to take Baelfire as a child.
But during this encounter, Rumple either does not know, or does not acknowledge Pan's true identity.
In Think Good Thoughts, when we learn Pan's identity, Rumple is not present at the time of Pan's creation.
During Rumple's present-day visit to Neverland, Rumple seems to know of Pan's identity.
When/how did Rumplestiltskin learn of Peter Pan's former identity?