I think you might find this previous discussion useful:

• Does looking back at history reduce the idea of national identity, or enhance it?

Charlemagne is likely my favorite example because who ought to claim him, the Germans or the French? The examples you chose are somewhat harder because, they all exist as nationalism, is taking off. German nationality pre-dates a Germany state and many scholars (Gellner, Anderson) have argued that nationality is ultimately about imagining interchangeability within limits. You can see that in some of these men’s careers, as they moved through various German states. It’s easy to think this is a thing of the past (was Kafka Czech because he lived in Prague, German because he wrote in German, or ethnically Jewish because as a Jew he could not “really” fit into either of the above categories?), but it’s still on-going. When Vienna-born Eric Kandel in 2000 won his Nobel prize, he insisted it was absolutely not an “Austrian Nobel” but a Jewish-American Nobel (his Wikipedia lists him as “Austrian-America” probably in part because Austria worked to try to get back in his good graces, for example renaming a prominent road named after the famously anti-Semitic Mayor of Vienna Karl Lueger). However, when, for example, Aziz Sancar won a Nobel prize in 2015, he quickly insisted it was a Turkish Nobel prize, quickly saying things like “I’m glad for my country,” despite being from Turkey’s Arab minority (his Wikipedia lists him as “Turkish-American”). In those cases, we often have clear sense of people classify themselves, not just how others want to classify them. But I think it’s important to think of it as: an active process, indentificafion, rather than than simply an identity, as the historical sociologist Rogers Brubaker has successfully argued.

My favorite Wikipedia entry used to be for Shah Ismail, the founder of Safavid Persia.

Ismail grew up bilingual, speaking Persian and Azerbaijani.[14][15] His ancestry is mixed, having ancestors from various ethnic groups such as Georgian, Greek, Kurdish and Azeri;[16][17][18][19] the majority of scholars agree that his empire was an Iranian one.[2][3][4][5][20]

You can see the layers of compromise there as different scholars put on different layerings, different imaginings, different ultimately categorizations of who he was. In his own lifetime, being a Muslim meant much more than being either Turkic or Persian. However, his Wikipedia page used to list him as Azeri, Persian, and Kurdish, if I remember correctly, each side with multiple citations.

Wikipedia has a whole page on “the Lamest edit wars” (their term, not mine) in Wikipedia’s history, and you’ll notice a lot are about nationality. Why? It’s not something that’s out there, but rather something that we classify people into. Some people, like Kandel and Sancar, make it easier by classifying themselves for us, but when other people fit into more than one box, people frequently fight over which box they “really” belong in. It’s not a coincidence that the very first section on the “Lamest edit wars” page is “Ethnic and national feuds”. Nation states have made this sort of classification quite a bit easier because they seek to classify what people really are from birth, but when looking backwards to an age before nation states, arguments are bound to spring up.