Customize your Participant Report to Show Number of Result Notifications for Each Participant
You can add a column showing how many result notifications each registrant in your Race has registered for to your Participant Report by going to Participants > View Participants > Report Options > Hidden Fields and checking off the box for Results Notifications and Saving Fields.
Now that you've enabled this field, it will be available to you when customizing this report under Report Options > Customize View > Pick from All Columns > No. Result Notifications Set Up. Once you have this checked, be sure to click the Customize button to save the changes to your report.
In your customized report you'll now be able to view the column with the "Result Notification" data.