seconding the alt timeline notion, because the first novel explicitly states that vampires had an entire underground society in place for when humanity nuked itself to rebuild society and rule
also dracula is explicitly stated to still be alive, and has reached literal cosmic deity levels of power
neither of those are really fitting in the standard timeline, since lesser vampires don't really get any mention and what mentions we do see don't give the impression that they're all unified (carmilla is devoted strictly to dracula, bartley as well, olrox wants to usurp dracula, and brauner was the starving artist in the corner by himself trying to rez who he thought were his dead kids)
not to mention CV dracula absolutely loathes humanity and has a whopping total of one human woman he got it on with after he became undead--VHD dracula seems much less hateful towards humans and made it a point of impregnating as many human women as possible (meaning countless given his status as a cosmic force) to try and darwin his way to a species hybrid that lacked vampiric shortcomings
not to mention the whole "transient guests" thing
VHD dracula has far greater ambitions given the things he prioritizes and tries to accomplish, and is seeing farther ahead into the future with his plans than the "fuck humans, i'm gonna rule shit and kill everything" mentality CV drac has
now, you write an alt timeline and it can kinda fit--but you'd have to do such a drastic rewrite of CV dracula's character to get him to the point of mindset that sacred ancestor dracula has, global vampire society and their unification and dispersal, human-monster relations, and the inclusion/exclusion of religious elements, that it wouldn't really even BE a castlevania universe anymore