well said and foundExcept, there is a distinction. As mentioned, in the newer books the Apocalypse Formations are called just that, while regular ones are just called Formations. Even Forge World stuff has the 40k ones specifically marked, and the ones that can be Lords of War listed out in a pdf.
Compare the Dataslate Formations. The 40k ones are called Formations, the Apocalypse ones are specifically named Apocalypse Formations.
In fact, looking at Dataslate: Centurion Siegebreaker Cohort, i see the following:
"If a Formation is referred to as an Apocalypse Formation, it can only be used in games of Warhammer 40,000: Apocalypse."
I feel logic dictates that Apocalypse Formations are still intended for Apocalypse only.