Really? Could you try actually reading what I've written?

    impossible to revoke without somehow maintaining a list of valid or invalid cookies

Completely true. A minimum date like you are saying is still "some kind of list of valid or invalid cookies". Or are you going to get into the semantics of "that's not a list"? As an example of something that you can't do without tying a database into it, I've seen sites that let you log individual computers out of the system from your account page. No way to do that without a valid/not valid check in the DB.