You are correct. The reason it was called "Diamond" was because the tour coincided with Frank's 75th birthay. Any 75th aniversary is referred to as 'diamond'. I hear that the tour was quite good. They even had commemorative sweat shirts for the concert. I got to see the shirts and they were pretty neat. It showed 3 pictures of Frank. One at 25, one at 50 and one at 75. It's yet another concert of his that I missed (I attended a university at the time and was too poor to go). Hopefully, it will turn up on video some day.