DaubianCossack: The province of Vidin is not wrong. I checked, and the city of Vidin is near the edge of the province (seeing as Vidin is on the Danube the border follows the river) but definitely within the borders of the province. Bor had pretty much no relevance in the CK period, if it existed at all, and didn't become a major town until the 19th century.
As for Nis, it's a borderline case. The province seems to have been divided between Bulgarians and Serbs, so could really be either. The city of Nis itself was Serb though, so I will change it to Serb culture for the next release. The Macedonian identity only really developed after the CK period, so I think they should remain as Bulgarians. Plus, I don't have any free culture tags.
As for Nis, it's a borderline case. The province seems to have been divided between Bulgarians and Serbs, so could really be either. The city of Nis itself was Serb though, so I will change it to Serb culture for the next release. The Macedonian identity only really developed after the CK period, so I think they should remain as Bulgarians. Plus, I don't have any free culture tags.