Just an FYI, there is a clause in the post island builder where it will only list topics that have a last reply time within the last month. I think that's contributing to your issue NewZealandNZ. What you can do is edit the cache_builders/post_island.php file. You'll see this line:
$one_month = $html->get_date() - (86400 *30);
Just change that to something like:
$one_month = $html->get_date() - (86400 *300);