the entry card

life - Questions about the entry card

I'm not sure how many of these entry cards I have filled in before entering China, but I always found the process fascinating. Now the procedure is going to be simplified and at least the Chinese do not have to fill in the card anymore.
Fortunately, that allows us to get some statistics on the card to support lingering questions. Last year 302 million entry and exits cards were filled in, 40 million by foreigners, who will have to stick to the habit.
Question: where are these cards? Where do you store 300 million cards a year?
Question: what is happening to them? Are they just stored or is a legion of people actually looking at them?
Question: when you want to find back a persons entry card, how do you do that? What is the system behind the storage of the cards?
This is for starters.