You are definitely not alone in this vent. For some reason people just don't get why they should RSVP. My wedding is in 2 months with the RSVP due date Nov 1. I put my current break down below just to make you chuckle. It may come off angry, but really I'm just laughing at how the guests make the wedding so stressful and probably don't even realize what they are doing.
Talk to your TA and encourage your guests to get moving
My Crazy List of RSVP Drama
* Sent out 143 Invites (DW and AHR in same invite)
* Mom sent me 2 more invites (4 guests) to add to the list yesterday
* 96 No RSVP
* 42 RSVP cards received back
* 5 RSVPs online
* 42 guests say they are booked
** 12 guests of the No RSVPs say they are booked
*** 8 guests of the above 12 are not confirmed as they didn't use my TA and I only heard from family who heard from someone else that they are going
*** 2 guests of the above 12 are getting married in a couple months and know how important RSVP cards are, but still haven't sent them in
*** The other 2 sent me an email saying they were booked
* 7 people still on the fence about going but keep bugging me about the prices that keep going up as we get closer to the date. No sh!@t sherlock, you should have booked when you got the STD or Invite months ago