@dimension10 Sometimes you ask for interesting requirements that make me search for a while. Searching for a bug, I have found a simple reason for this effect. I have set up the event log together with the installation of this plugin at 2014-03-06, so this is 26 days ago. To compute the number of weeks, the plugin computes floor (number of seconds / 604,800 ), where 640,800 seconds are 7 days). So today, we see as a result "3 weeks ago". The plugin works fine, there is no bug.
By the way, today the event log has registered 35,758 events in these 26 days. If we set for infinite history, the creation of the history page will take a considerable time, the user has to wait for (may even once trespass the time-limit of PHP). But as you say, we may cross that bridge when we come to it.