It's a myth though. The developers have always planned to make a separate title that is not part of the numbered series.
Here is a quote from Shinji Mikami:
"We sincerely apologize to the people who anticipated Bio Hazard 2 for Saturn. We were developing Bio Hazard 2 for Saturn, but found out that it's difficult to achieve the same level of quality on the Saturn that the PlayStation version had. So we decided to change the platform (from Saturn) to Dreamcast, and develop a new game called Bio Hazard Code: Veronica for the system. We are working like mad to make the game better than the PlayStation version visually, on the scenario side, and the overall game itself. Thanks for your understanding."
This quote was published on October 21, 1998. Here
is the source.
And here Mikami-san also explains the reason why the game doesn't have a number:
"This time, there's no '3' or '4' in the title. Veronica is a character's name. The reason we didn't use '3' or '4' is because we wanted to make an all-new BIO, including the visual aspects, etc. However, that doesn't mean this game will be a total gaiden. It's a secret, but... the story is a continuation of 'BIO2'... isn't it? (laughs)."
So the developers never had the intention to make the game numbered. It's a gaiden (spin-off) as well.
I believe it was called Biohazard Dreamcast before getting the Veronica title.
Mikami-san also said in various interviews that Veronica for him is the true BIO3 and the true BIO4. He even mentioned once that this game as a whole is the only true BIO game in the series.
And it's just his opinion, which is irrelevant to the topic. What we are discussing here is simply a matter of definition. And you can even see above that Mikami-san himself said that Veronica is a gaiden because it is. Yes, not a total one, but still a gaiden.
I personally think the story of Revelations 2 is more relevant than the story of Biohazard 6, but the thing is that big-budget titles get numbers. And if you are making a big-budget title for a mass audience, you want the maximum number of players to be comfortable with the story that the game tells. Therefore, no one needs to play Biohazard 4 to understand Wesker's character in Biohazard 5, since the new narrative does not rely on the previous one, since it changes the character's goal and explains this part.
In other words, Albert may be a million times an old character, but functionally he is no different from Alexia, Carla, Miranda and so on.
This, of course, does not mean that numbered games do not contribute to mythology and are not related to each other. They do all these things, just not in the foreground, otherwise it would make it harder for casual players to enter the series. And nerds like me who dig deep are a niche audience that won't recoup the costs.