I find your question interesting, and not just because of the Viking era before the existence of modern countries. My grandmother was born on an island on the west coast of Sweden. So she's Swedish. However, it's a narrow and not entirely accurate description of her historical roots, even though her ancestry is statically tied to that island. Her ancestors have lived on that island for well over 500 years. In the 1600's it was transferred to Sweden. But before that, it was ruled by Norway/Denmark, and the folks on the island still spoke Norwegian until the 1800's. A very distant great uncle from there was even Chancellor of Norway. In historical times, when people moved to the island they came from Norway, Sweden, and Denmark. On DNA tests, we show more connection to Norway than Sweden. So for that south Norway/west coast Sweden/Denmark area, just saying Nordic is more true than trying to pick a country.