Unreal, that kind of mistake just makes you want to scream. It's like @the_barbara said, those lost clues are a total gut punch. My advice? You have to treat every site like it holds the only copy of a priceless book. Standard practice now is to move at a snail's pace with trowels and brushes anywhere near important layers. Blasting for speed should get you fired on the spot, no questions asked.
Feel sick just thinking about it. All that careful work by people before them, and a real piece of history, just lost for good. Tbh, it's worse than just losing clues, it's like burning the only map. That damage is final, and you can't get it back.