Mya seemed to have sourced their FOUR FLIES release from pristine or neg source material, which they must have obtained from somewhere semi-legit. I wonder whether they've just decided to deal directly with licensors/materials-holders from Italy - and maybe pay them directly for the privilege - and blithely skim over the issue of US ownership. For all I know Argento's company is getting a cut from both the FOUR FLIES and DOOR INTO DARKNESS releases, with both parties giving it a shot as long as no-one directly gets steamed. The FOUR FLIES disc wasn't exactly an under-the-radar release and if Paramount were incensed about having their baby stolen from under them, they've had ample time to do something about it.
Regarding HORRIBLE, upon reflection I suspect I could care less if it's properly licensed from official source channels via MGM. If they release it from original source materials and do a good transfer, that's good enough for me.
Maybe Mya is bribing staff members at Paramount and MGM with whiskey and fine Italian hookers to keep quiet.