Cool thanks for the reply @brybro27 ... funnily enough , first thing I did after I posted was to go check that out haha. Probably should have did that first before I posted :).
For each airdrop, there will be a minimum amount required to get a guaranteed airdrop
The amount required is announced before airdrop is dropped
Amount changes per airdrop and what rarity the card is
Legendaries require a higher amount, epics require less
The above part added a bit of confusion. Especially the line about the amount changes per airdrop.
Anyways , the question now is : if one buys 750 packs , which should equal 15 promo cards ... do you get 15 copies of the first promo card or are you getting all 15 promo cards?
I would assume it's the latter , but hey ... ya never know ...
Buying 750 packs during the pre-sale will get you at least 15 (1 BCX) of the exclusive promo card.
After this exclusive promo card and pre-sale, there will be 13 other airdrops that won't stop until a new milestone is achieved when selling out Chaos Legion packs. My guess is each milestone will be 1M more packs sold.
So when each milestone is reached, an airdrop will occur. The airdrop will work very similar to the promo card airdrop, however, the guaranteed amount of packs required will increase quite a bit (I'm guessing around 300-400 first airdrop).
After the first airdrop, the subsequent airdrops will always increase in guaranteed amount required as all packs bought since the pre-sale count towards these airdrops.
So if you buy 750 packs during the pre-sale, those 750 packs will count through all 13 airdrops. That is why buying early in pre-sale is pretty significant as you will get a chance for all airdrops through the public sale.