[Wow.......picky fellas in France........just like in Denmark! ]
No its when imported to the Netherlands. French laws allowed the car as it was sold by Ford + that riveted plate.
The dutch were in the end not that picky, its just you need take them carefully by the right side, pick your words and act as you almost agree with them
Plus most existing laws regarding old cars are forgotten as they are likely not even in their IT system.
Personally, I would have not added the light this way, I would have double taped some small modern led turn light underneath the mirrors, or replace with modern mirror having them like audi's and many others have. And first thing out of the import location with papers in hand, removed them.
Back in Paris in the early 90's, on my bike, got stopped and fined for having a clear white headlight. I simply refused to use the ridiculous yellow coloured ones that were reducing the sight greatly. All cars and bikes were using an extra yellow bulb around the glass bulb... supposed to prevent blindness of other drivers...
In the end just before I couldn't delay the fine payment anymore, law changed and got letter saying I was exempted of the fine, because I was now to be fined for having legal lights
I follow in big lines most of laws, but when they are stupid, to me, laws are made to be bended