In my experience the typical perception is that you’re X when your parents and grandparents are all X, hopefully also great grandparents.
There is a lot more melting recently. Europe historically has been pretty big on cultural identity because everyone had/has a grudge with their neighbors for trying to assimilate them at the edges.
Slavs for example (I’m from Slovenia) can trace or Slavic lineage all the way back to the 600’s and the fact we haven’t been assimilated into German or Italian despite being part of their countries for centuries is a point of pride.
There is still a recognized small German minority in Slovenia from back in the 1300’s when they tried to deal with the slavic problem by encouraging people to go settle in our area, which was part of the Holy Roman Empire but we of course wanted to keep it Slavic.
To be fair, as late as the 1940’s the germans were trying to germanize the slavs.
Some of these grudges are very fresh and ongoing. Look at how the Catalonians are fighting against being called Spanish