I have never knowingly lied about a PS/ADR and also never had an issue with a lost reservation, but I did have one experience with CRT where I truly thought I had a PS, but it turns out that I did not.
It was back in 2000 (when things with the CRT breakfast were crazy, but not as crazy as they now appear to be). We were staying YC concierge, so I had the planners there make all the PSs. Among the requested PSs was a CRT breakfast a particular day. I was never informed that the PS was not made, so I assumed that it had been. When I checked into the hotel, I got a print out with the list of all the PSs and the CRT breakfast was listed on there.
So, I go to the castle on the appointed day, only to be told I had no PS. They called us up on the computer and had a list of all our other PSs, but there was nothing on there for CRT that morning. I did not have the PS print out with me, but I kept insisting that the YC concierge had made the PS. Thus, after a few minutes, they agreed to "slip us in" and, after a very short wait, we proceeded to have our breakfast in the castle.
However, upon return to our room, I found the print out with the list of PSs. I had not looked at it closely before. Sure enough, the CRT breakfast was listed there along with the other PSs, but there was a note that said that someone from the concierge desk needed to call to confirm the PS. So, apparently, I did not have the PS i thought I had after all. It was all an innocent mistake on my part and, in retrospect, I appreciated the fact that the CMs at the breakfast had been able to slip us in after all.