If date stamps were so cool, what is to stop people from doing it on any book at any time?
They add zero value.
Not only that, I suspect a grading company would be able to tell if a stamp was added recently.
"“All men having power ought to be distrusted to a certain degree.” - James Madison, 4th President, United States of America, architect of the Constitution.
"I'm going to say the list is biased towards collectors born yesterday." - Dr. Balls
"This is the lowest example of class that I've ever witnessed on the boards." - bronzejonny
"DESSLOK, desslok desslok,...."