...yes? It's how it works in the real world. Maybe not with a giant conference of all the scientists ever, but the handful that make the revealling discovery will publish a paper on it, maybe hold a conference, and after it's verified by others it's accepted.
Same way we reclass a scientific discovery every time we learn something new. Nobody just -knew- there was a variant of mold that could be made into Penicillin, Jonas Salk labored over heavy research before finding that out on accident.
I like to pretend they just didn't have enough data yet, and that with the new generation, new technology, new knowledge, and more Pokemon to get data from, they finally can say, "Yeah, this is another category for Pokemon for sure, and going through our old research data, it would seem these Pokemon as well, are x-type."
Just like science is in the real world. Things are re-categorized as new data becomes accessible. We can't just know everything, right?