How does the iPad handle recent resources?

I have been using the iPad version since it first came out, but have never really found the list of recently used books to be helpful.

First, it needs to have the option to be cleared, and second, and more importantly. it does not seem to work correctly. Books I have not touched in weeks are still near the top of the list, but some books that I have downloaded to my iPad and have been reading over the last few days do not yet appear anywhere near the top of the recent books.

I assume I am doing something wrong, or have misunderstood. Could someone clarify how this should work.

Many thanks

karl