I modified a reminder in Outlook, and as I was preparing to delete another reminder, the modified one popped up. This caused me to accidentally delete the wrong reminder, and I had no idea which one it was. So I wondered if there was a way to figure this out. Please note that I have not tried this for Outlook Calendars that are stored on the internet.
If you are running Outlook 2013 or later, I think there is a solution — of sorts — to finding a dismissed reminder. If you run into this situation, here’s something you can try. Go to your Outlook calendar and click on the menu “Search Tools” and then “Advanced Find”. Then select the “Advanced” tab in the find dialog. Now under “Define More Criteria” select “Date/Time Fields” from the “Fields” drop-down and then “Modified”. For “Condition” select “Today”, or “Yesterday”, or whenever you accidentally dismissed the reminder.
Click “Add To List” and then “Find Now”. Outlook will search and find Calendar items that you modified today, including those reminders that were dismissed. At least it did work for me when I tried it. I hope it works for you.