More of an observation than a question, but it does make me wonder if DXV realised this when he designed the cards: in a 3+ player game, since Masquerade doesn't instruct you to reveal the cards after passing them around, you don't know what cards are in your opponent's decks any more.
Also, theoretically Rogue/etc. can gain from the trash, and don't instruct you to reveal the gained cards, and other players can't normally look through the trash (I think?). Theoretically they can play Rogues themselves in order to look through and therefore find out what card you took, but they don't always have the opportunity, and if two cards are gained from the trash by different players, in between your trash-inspections, it may be impossible to know who has what cards in their deck. (An edge case when the gain-from-the-trash card is from the Black Market so the other players can't inspect the trash at all).
That has implications for counting the score; primarily, Curses and Estates get passed around, but also you might want to pass a Duchy, or another Victory card better than Estate, if the rest of your hand is exactly the right treasures for buying something good. (As an edge case, a lot of Rabbles followed by Minion and then Masquerade may well force you to pass a green card, and maybe you trashed the estates and only bought Provinces...). Good Victory cards are often in the trash because of being Expanded, or even just remodelled into themselves in the endgame, so Rogue/etc. can also secretly change the score. (Edge cases for gaining from the trash include Silver for Feoda, and Action cards for Vineyards).
Mainly just wondering if that effect is deliberate. Isotropic used to have a score counter, which might therefore actually reveal information to you that you couldn't have known just by watching your opponents very closely and having a good memory.
Edit: I should read the rules - "A player is allowed to count how many cards are left in his deck, but not his discard pile. A player may not look through his deck or his discard pile. A player may look through the trash pile, and players may count the number of cards in any pile in the Supply." So Masquerade is the only one, huh?