ToxicBunny
Oi! Leave me out of this...
maybe its hard to get the limestone originally used,
architects are long ago dead,
exceedingly hard to make something meet building codes and look beautiful
and maybe just maybe, they might decide the building needs to be modernized.
So they would use newer limestone.
So what, they have the plans and many decades of photos and scans. They don't need the architect.
A building like this being a heritage building does not need to meet building codes in the way you're thinking.
What part of your brain thinks the French would want to modernise a building that draws 13 million people yearly to Paris?!?!?! I don't even being to comprehend how your brain came to that conclusion.

