We invited 110 total. We ended up with 99 yes and 11 declines.
Our RSVP deadline was September 9th. By the end of day on 9/9, we were missing 3 couples RSVP’s (so a count of 6 people). We had all of them in my the next day. Overall we were very pleased with the quick reply’s and surprised how many yes’ we got! The 20% rule definitely did not apply in our situation.