This problem can cause a great deal of confusion.

When the avatar server that is hosting your event is reset or crashes (which usually happens in a completely transparent fashion, it's down and up again before anyone even knows it) the record of anyone who came into your event before the reset is lost. Thus, the e-mail is incorrect.

However, your event host skill is recorded on a minute by minute basis, and is not affected by this. Your event host skill is being recorded in real-time, so you get full skill for everyone who is in the event.

In short, if the end of event e-mail that is sent out is wrong, there is nothing to worry about.