the theory is that they tend to make new models for an army in bulks and not one off (unless it’s the obligatory foot heroes) and models release during the end of editions narrative supplements are sometimes teasing the future.
if it hold true it be
FS, Nurgle, Gitz (well they got 2 releases), SCE (well duh), Sylvaneth, Soulblight, and DoK.
i guess for their sake we can count the Gorger release for Ogors to be in there even if Ogors didn’t officially get a Dawnbringer release.
IJ, FEC, and Slaves are questionable since they got full or big releases during Dawnbringers.
of course they maybe smaller releases like NH and Sylvaneth from last edition but just more then one hero (honestly I think NH stuff where actually Soul wars leftovers)