I still don't buy the explanation that that GW started re-naming their ranges because of Chapterhouse.

GW calling Space Marines Adeptus Astartes, or Imperial Guard Astra Militarum does nothing to stop a Chapterhouse-alike selling Space Knight shoulder pads or Imperial Trooper heads - as evidenced by all of the 3rd party sellers who are quite happily selling models/parts which are blatantly based on GW models/designs with no legal problems. The problem with Chapterhouse was that they were selling models as actual Space Marines or actual Imperial Guard.

I find it more likely that GW wanted to make their Imperial Guard more distinct from Start Wars Imperial Guard or the historical French Imperial Guard, and their Orcs more distinct from Warcraft Orcs or Lord of the Rings Orcs (etc. etc.), while at the same time thinking that putting more pseudo-latin into 40K makes it more grimdark (confusing this for depth and/or maturity).