And the faked messages the Gorn were creating (using a very complex and personal Commodore Travers) just seconds before Kirk and Co. beamed down to se Cestus III destroyed showed the Gorn had a lot of detailed info about Starfleet, The Federation, and its personnel. The did a completely normal Federation standard approach; and opened fire before anyone at the Base could do anything. The Base even tried to surrender (and stated they had civilian women and children); but the Gorn just wiped everyone on the base out. Its also clear they knew the 1701 was the ship assigned to patrol the area and designed this trap to lure them into a test; and possibly destroy them.
It's also pretty clear that they didn't recover much info from the base as the one survivor said they just came in and 'poured in on' until there was nothing left.
So - how and where did the Gorn get the majority of the info it had of Star Fleet and The Federation? Probably from Federation ships and crew the Gorn captured here and there as more Federation ships passed through Gorn territory over the years leading up to the Cestus III incident. As La'an related; she (and the Gorn) didn't expect her to survive; and it was sheer luck a Federation Starship (and Una) came across her. Also, given the situation and the mental trauma she suffered, Federation medical personnel aren't convinced everything about her story or her recollections are accurate or real.
