Please take a look at the screenshot attached. It was taken from a recent Seasonal Match. My opponent had just played one of the witcher cards that drag the other two of the set from the deck to the battlefield (Eskel, Vesemir, Lambert). I then destroyed the 3 cards with Arachas Venom. The screensot shows that while my total deck count of 25 is correct, the deck count on his pile did not lower for the two witcher cards that were drawn from it. His total card count is 27 because of it.