I was born in Canada in the 80's and my parents gave me the family name Y X where Y stands for the family name of my mother and X stands for the family name of my father.
Then in the early 90's we moved to France and my parents had to do the "Transcription de naissance" (transcription of birth). There was a problem, however, because back in that time it was not possible to give the family name of the mother to her child. Hence my parents had to register me with the name X and not Y X like I was given in Canada. This made me having my family name differing on my Canadian and French passports as well as on official documents, i.e. my family name was different according to the country I was in.
However on my French "Copie d'acte de naissance" (birth certificate), despite my "Nom" (family name) showing as X, there is a mention stating that my parents gave me the "nom patronymique Y X". And now that I must renew my ID card (carte d'identité), I fell over an official webpage https://www.service-public.fr/particuliers/glossaire/R10114 which states that the "Nom" (family name) is also called "Nom de naissance" and "Nom patronymique". Therefore I understand that my family name according to France could well be Y X? If this is true then I'd like to modify my passport to show my "real family name" because this problem caused many problems when I lived in South America and also when I had a son and wanted to give him the family name X.
So right now I don't know what my family name is in France. Is it X or Y X? If you could shed some light I'd be happy.