def card_names(a_deck):
    return [card[1] for card in a_deck]
  
all_card_names = []
for deck_card_names in [card_names(deck) for deck in decks]:
    all_card_names+=deck_card_names
    
len(all_card_names) #17052
all_card_names = set(all_card_names) #make them unique
len(list(all_card_names)) #642