I had the same issue with my ds's birthday party. We invited all 29 children from his Kinder and 3 days before the party I still hadn't heard from 12 parents! Such a huge difference as to whether those children were coming or not. I haven't looked at who came vs. who RSVPed, but I think the 12 who didn't RSVP didn't come. I thought it was cause his party was in the middle of Jan and the invites had to be given out in early December that it was a problem, but from your issues it seems that's not the case . So sorry you're struggling to work out your numbers. I was going to send an SMS to the parents who hadn't responded, but I couldn't find the list of the kinder parents contact details, so I just had to guess. We had heaps of stuff left over!