To me, this fact is direct evidence of it being a later addition, and probably a fraud. The author describes the first part of the text as being excised and expertly written. By excising text, and carving a frame around it, the carver is weakening the rock at that point. An experienced carver would have chosen a rock strong enough to fit the inscription. While the rock was strong enough for the original text, by removing the frame and adding another line, the rock was weakened even more, beyond what the original author had allowed for. Had the whole text been the product of the original author, he would have chosen a thicker, stronger starting material. But if this is a later addition, the second carver had to work with the material he had, and created the weak point by his addition, at the point of his addition.
But that was 2 thousand years ago.
As of LAST WEEK the piece had no damage whatsoever. It was photographed extensively last week before the airplane ride.
The experts will have to weigh in, but the fragile, brittle 2000 year old limestone was just fine as of last week.