Yes, they do, if all the messages are read in the topics. Then it shows a "more topics" if you want to go back further. However, it will display all the topics with unread messages in them (even if this is more than 5).

If you're ending up with a lot of unread topics you don't care about, the answer is to mute that topic (you can mute a single topic without muting the whole stream, which is awesome but a lot of people I've worked with didn't realize you could do this).