Not sure when this came out nor which Outlook version (2013, 2016, 2019, Click to Run) is getting it, but a new settings has been available to automatically dismiss reminders for past events.
This is quite handy as one day or another we all faced the situation where we were getting reminders for past events.
To enable this option, go to File\Options\Advanced from your Outlook client and check the Automatically dismiss reminders for past calendar events available in the Advanced section
