If the cron has run and the values haven't changed, then the values would presumably be correct based on what is expected. For example, you suggest that the latest member hasn't changed, but looking at the "newest members" widget on your site, the latest user there matches what the stats say. Presumably you're seeing users who don't have "valid" accounts and thus they aren't counted -- this is the correct/expected behavior.
Beyond that, the only other thing is an add-on that has interfered with thread/forum count updates themselves, as the statistics come from those sums. You could try rebuilding thread and forum info and then running the cron to see if the count changes. If it does change, then it's probably an add-on issue.