There are a couple of reasons why the total number of people listed here may not be completely accurate.

1. Sometimes event organizers receive mail-in registrations and those mail-in registrations may not yet be entered into the participant list.
2. If a person is intending to do the race but hasn't yet registered, they may manually still add the race to their imATHLETE profile, which would put them on the participant list.

I hope that helps explain it all for you!