Sorbs and Balkans Serbs are not same people,
Sorbs were not part of Serbian tribe from eastern Germany they lived north of Serbs. Sorbs adopted Serbian name because they were in state federation with Serbs, name of Sorbs before they adopted Serbian name were Wends.
Serbs came from eastern Germany in VII century, of course that modern Serbs are not 100% same people as Sebs from VII century because of mixing with native Balkanites.
Same is with Croats, modern Croats are not same people as Croats which lived in White Croatia.
Western Ukrainians, Rusyns and southern Poles are closer to White Croats than modern Croats from Croatia.
Modern Magyars are not same people as proto-Magyars.
Modern Tukish people are not same people as Oghuz Turks.
Modern French are not same people as Franks.
Modern Germans are not same people as ancient Germanics.
Modern Italians are not same people as Romans.
Modern Greeks are not same people as ancient Greeks.
Modern Spaniards are not same people as ancient Iberians.
Modern northern Indians and Pakistanis are not same people as ancient Indo-Aryans.
Modern Iranians are not same people as ancient Persians.
Modern Egyptians are not same people as ancient Egyptians.
Modern Mexicans are not same people as Maya and Aztec people.
Modern Finns are not same people as ancient Finno-Ugric people.
Modern English people are not same people as Angle and Saxon tribe from Middle Age.