Ah right
OK, so if it's OK I should really explain what I need again because I think I may have been unclear.
What we have now is so close to perfect, this is what I need:
People upload events as normal
Then, when the even is online the attendee button is automatically shown to everyone, ideally like in the image attached.
When they click 'Yes I was there' then they either have to log in, or if they are logged in they go on the attendee list for that event.
I hope that makes sense, it is a simplified version of what we have, basically, the Yes I attended button is always there and when clicked you are added to a list of people who went.
Thanks