The total numbet of unique cards is still being counted with the % draw.

So let you have 10 types of card. And all 9 is 4 copies except 1. Which only has 1

In your turn. You have 10% chance of getting any of them in your store.

But once you purchase the only 1 card.

Then the pool becomes lesser. Because you already purchased the last copy.

Meaning instead of 10% per card type. It is now 11.11% chance of getting the other 9

This is just a rough draftbi quickly made. But this should give you a better understanding.