Not to mention there are references in gamefiles from P3, to be more specific its MGs.
To be fair, there's also a partially functioning "Panzer III" in CoH2, but it uses the Panzer IV Ausf. F1 as a placeholder, and doesn't have a squad assigned which results in the AI being horribly broken if you attempt to give it any order. I think the All Units Mod has a working version of it, but still has no model, it's only a Panzer III as far as the unit name and stats.