It's a forum option, it only shows posts made in the last 30 days.
If you go back to the forum page, where you can only see the 6 posts, look at the bottom, and change "Showing 7 of 7 topics sorted by last post date in descending order from the last 30 days", to "Showing 7 of 7 topics sorted by last post date in descending order from the beginning".