I agree with your statememt about Alans.
I insist on my opinion considering Slavs during Migration Period, however, mentioned names could be borrowed to name related later ethnicities and/or political subjects in the same region, e.g. “Scythians” used in Byzantine sources to name Goths, Alans, Slavs and various Turkic nomads in Pontic steppes. Or “Regnum Teutonicorum” to name East-Frankish Kingdom before HRE and, as we use in AoE II community, word “Teutons” to name medieval German states in common.