The new books each day are added to the top of each list. Once you hit the books you saw yesterday, you can stop. I will delete books as I have time to check they're no longer free. **I would love it if someone or several people in the US could volunteer to help with this occasionally, as it takes so much time for me in Canada to check whether books are still free in the US. Amazon makes it extremely complicated.
Some books that will end up at the bottom of the different lists are long-term free.