I have not verified that this still exists recently, but here is the problem at least as I had noticed it in the past:
1. I trade cards and kill a player. I receive his cards, one of the cards I receive is a card I just traded.
2. I have a card for a specific territory which another player owns. The other player trade his cards in and gets a +2 bonus on that territory. I still have the card in hand.
3. I trade cards and the next card I draw is the same as one I just traded.
Conclusion: For points 1 and 2, Cards are unique per player instead of unique per game. it's possible for players to be holding the same cards where as in the real world, there is only 1 for each territory and 2 wilds. How I never received duplicate cards when killing players confuses me. Does the system regenerate what cards they had when cards are traded over?
I am not sure if this was fixed already. Like I said, I haven't noticed it recently but I haven't been thinking about it either. But the cards definitely need to be unique, and they should simulate an environment where they come in a certain, randomized order and then when the deck is replenished/shuffled, used cards will become available again. Point 3 showed that cards were randomly generated and could be any card at any time. While this is not as crucial as the first 2 points, there should be an understanding that if you had a card before that you're not going to get it again right away.