I use the 3 criteria under registration as follows:

If I globally add registrants to an event  I put that under the invited field

If they RSVP Yes - I mark as registered

If they RSVP No - I mark as Do Not Register

This way I can determine who has replied versus who hasn't

Is this what you were asking?

This also puts them in the queue to be 'seated' if the event has seating

 We used the same format.

Registered = Accepted

Not Registered = No response

Do not Register = Declined

Thanks Laurel

That helps a great deal!

Thanks Charlotte

Your answer helps too and is basically what we are doing. 

The reason I asked, I was told to always enter a date when I added a person to an event and you can only enter the date if you mark the person registered.

We are often given long lists of complimentary attendees and we enter them in the events module in case they show up and have not replied or registered.