I posted last week in a tizzy because I had received two empty RSVP envelopes. When preparing invites we learned the adhesive on the envelopes was pretty terrible and requiring pushing on them for a few seconds to get them to stick, which was already a pain.
Update: I spoke to my parents Friday and their invitation came in the mail with the flap open. The invite was there but the RSVP card and RSVP envelope were missing. I'm so annoyed and trying not to panic. Thankfully I received 4 RSVPs back successfully in the mail Saturday but I still worry that some guests won't get the card or that I won't get their returned cards.
PSA: Be CAREFUL with Cards and Pockets envelopes. I bought them at the enthusiastic recommendation of my Etsy invite vendor and I really regret it. They weren't dirt cheap either! At least use a sticker or tape or something to keep them safely shut.