Okay. Here is the original text from the SNES game's opening text scroll.
Every one hundred years the forces of good mysteriously start to weaken. Thus, the power of Dracula starts to revive itself. His power grows stronger and stronger every one hundred years.
Dracula has revived many times. However, his sinister actions have been consistently thwarted by the Belmont family. It's been one hundred years since the last confrontation between Dracula and the Belmont family. But now the serenity of Transylvania is being threatened by destructive forces.
On a dark and eerie night Dracula rose from his grave to unleash his destructive power over the countryside. Once again Simon Belmont is called upon to destroy Dracula. With only his whip and courage he sets out to restore peace to Transylvania.
Well... Can't say I recalled the blurb about it having been one hundred years already since the last encounter. But then, the only real thing separating the overall gist of the opening introduction in the English version from the original Japanese version is the line, "Once again Simon Belmont is called upon to destroy Dracula." Other than that, the story does pretty much establish this as a remake and not a sequel.
However, the image of Dracula rising from the same gravestone seen at the conclusion of CV II combined with the fact that Dracula is VERY very under-powered in the game's final match does keep the idea of SCV IV being a new adventure for Simon firmly embedded in my mind.
As for the whole hundred year rule thing. . . Random script writers' ineptitudes aside, Japan is notorious for restarting a series from the point of a brand new title numerous times ignoring many of its previous installments. Godzilla is a solid example of this. 10 years after Toho's last Godzilla film in the late 70's, the monster was treated to a rebirth in 1984 that took place 30 years after his very first movie and retconned all of his previous outings in between (more than a dozen films at least). This was the beginning of a darker, more serious Godzilla series that ended in 1995 with the creature's death. Four years later, the Godzilla Millennium series was launched introducing a newer, more menacing design for the beast and a more slick, stylized format. Once again, it alluded to the idea that the majority of the monster's previous outings had never happened and that Godzilla has simply always been around since awakening in 1954. Curiously, the entire Millennium series is comrpised of movies that restart the series over again. That is, each subsequent film is a direct sequel to the first movie ignoring all movies in between. This changed with Godzilla: Tokyo S.O.S. which is a direct sequel to the previous film Godzilla Against MechaGodzilla. All this came to an explosive halt when Ryuhei Kitamura mounted Toho's 50th anniversary Godzilla film - Thus far, the last in the series. Godzilla: Final Wars pulled a full J.J. Abrahams-worthy 540-degree turn by revealing in a flashy five-minute opening montage that EVERY Godzilla outing had not only happened, many of its key moments were now repeating themselves and all leading up to a final penultimate battle royal. Proof positive that with a little ingenuity (and a bit of fun), any plothole-ridden series can be fine-tooled and reimagined into a working, cohesive whole.
Now as for Castlevania, as far as I've been playing the series the way that I've ALWAYS understood the hundred-year rule is that it does not exclude other attempts to raise Dracula by various other means. Human sacrifice, spirit-transfusion, mind-control, black magic, tampering with the space-time continuum, all are perfectly good methods of raising the lord of all vampires as far as I'm concerned. Never once was there a mandate that explicitly stated Dracula and his castle could ONLY rise once every hundred years. No, once every hundred years the barriers separating our world from the realm of darkness weakens of its own accord and evil is allowed to break through since it naturally grows stronger and stronger over time. Dracula is a manifestation of ultimate evil. The Demon Castle is a manifestation of it as well. He claims the most steady ownership of its power and thus they come back every hundred years whether we mere mortals want them to or not. Aside from that, there is nothing stopping servants of evil from doing their darnest to raise the dark lord prematurely whenever the urge takes them. When you factor in how many other possible threats could be lurking in the void of chaos that even a Belmont would have a tough time putting down, the possibilities of future CV titles really is limitless.
...A shame though how some people just don't choose to see it that way.