It does make a kind of sense: there would certainly be rumors and unofficial contact with an alien species decades or centuries before anything official took place - involving thousands or perhaps millions of people before the folks from Starfleet got to it. But once the official cat was out of the official bag, the old dots would be retroactively connected.
I'd find it
less believable if our primary heroes were aware of every species in or around the Federation, or even possessing sufficient knowledge and insight to look them up in the databanks.
Timo Saloniemi