And then from that point forward, everyone treats it as common knowledge. This happens regularly in serialized drama, sadly. (To give another Trek example, it was a big revelation that Data was created by Noonien Soong in "Datalore," but subsequent episodes like "The Measure of a Man" acted as if everyone knew who created Data all along.)
And even worse, they then cast Brent Spiner as Noonien Soong, so it should've been even more obvious that he created the android who looked exactly like him.
Another example is holodecks: in "Encounter at Farpoint" Riker reacted as if he'd never seen one before, but VGR established that Janeway -- who's the same age as Riker -- had grown up with Flotter & Treevis holoprograms.
Then there's the similar problem with warp core breaches, which were introduced in "Contagion" as an incredibly unlikely, unprecedented malfunction, but which soon became so commonplace that it seemed all you had to do was cough in the direction of a warp reactor and it'd blow up.