You would expect the news would report something like "055 Destroyer," "094 ballistic nuclear submarine," "075 amphibious assault ship." Particularly 31 Hainan is the first of its type, you would expect something like "31 Hainan is our country's first amphibious assault ship" etc. These are all for normal practice of news reporting. Yet if you listen to the CCTV news, PLAN commissioned a 031 ship, a 105 ship, and a 18 艇 (there is no equivalent one-to-one translation for this word in English, it could be submarine or a fast boat). They even didn't want to utter the word "submarine."
Now, obviously it's not because they wanted to hide the types of the ships since they're quite clear from the video. It also has nothing to do with whether "we know or not here at SDF."