No, you don't have to.
But if it were me, I would. I certainly would on a big ticket item like an old SA highgrade book with a four grand asking price. Indeed I did so the one time I sold a book that fits the bill. And if you don't, and someone else knows that it used to be graded two units lower, be prepared that they might provide the information that you've chosen not to.
Bob, that is part of the issue as I see it. Whether you are right or wrong being left completely aside, if this becomes the precedent, then the precedent that is set is not just going to obtain for multi-thousand dollar SA books. If the consensus is that this is an issue (like pressing was) then it will be important to be consistent across the Board.
And even though I consider it to be a non-issue (as i did pressing) I will provide in my sales threads all the information that the Boards determine to be appropriate.
So is Bob an outlier, or is this something that has consensus?