Intact historical buildings and artifacts are rare, because something like this is the expected outcome. People are careless and incompetent, except by accident.

Restoring a major historical building is always a one-off project. You follow the best practices, and the chance of a catastrophic outcome may be 10%, 1%, or 0.1%. You can't tell those scenarios apart in advance, because they all look very similar. Success is overwhelmingly likely. If a catastrophe occurs, the reason is often obvious in retrospect, and you will take that into account in the next project. But it clearly wasn't obvious in advance.