Hell, maybe the data on the cybernetic aliens were encountered were considered so important and classified it was loaded into the top secret central memory database that the Federation created to store their most important knowledge, Memory Alpha. Which was then wiped out by the Zetarans in the TOS ep Lights of Zetar. One thing that is very apparent, as is often the case in scifi societies created prior to the information age. The level of constant access and dissemination of information that we enjoy in the 20th century is greater than that in this fictional universe. Of course, the planet blew up back in 1992 (IIRC) according to this timeline.