I have noticed this as well. And it was related to the battles. If I or someone I had a partnership with fought a ship I knew about the tech it had. Otherwise not.
In addition if I used technological espionage to find out what techs an AI had it didn't update the listing. It told me in the logs what I found out but in the diplomacy screen it didn't update it. Had to use paper and pen to keep track of em so I knew what to steal.
