Yea good question, we should have been more clear about this in advance. The 5 airdropped cards will be in addition to the 20 cards already revealed. That means that once all 5 airdrops happen, there will be a total of 25 cards in the set.

There will be 300k dice available in total, and an airdrop will happen each time 50k dice have been sold, except for the last 50k.

The details of the cards to be airdropped are still TBD, but in the case of a Legendary rarity card (which I would say is likely) it would be expected that on average 1 in 150 dice purchased would receive one of the airdropped cards, so 150 would be the amount for a guaranteed card in that scenario.