Shower Invitation Question!!!???

LCLaw3

So last night I found out that a person that I invited to my shower never received their invitation.  This made my husband go crazy since it was his long time best friends mother.  I plan on sending another one out, but I triple checked all my invitations before they were sent out and had special address labels made, so I KNOW for a fact that it went to the post office.

Today, come to find out, one of my co-workers didnt receive one either!!!  Not only is this embarassing, but now I'm stressing out about how many other people never received their invitation....worst part is, the invitation says "Regrets only", so unless I personally call each person, I won't know who got one and who didnt...and that brings to everyones attention the fact that some people didnt get invitations. 

At this point I'm blaming the USPS because I know for a fact that these people (everyone on my list, really...) was to receive an invitation...but that doesnt help me with this dilemma.  Has anyone experienced this problem?  How do I fix it?  Plus, what to do about whether people got invitations or not!?  TIA.