Interesting. So for you, a character's continuity can be different for each person. Sort of like "continuity is what I say it is."
Jesus Christ dude.
Spider-Man's 616 Universe comic book continuity is controlled by Marvel. They produce the stories, and we as readers accept that they decide what is and is not a part of that continuity. Empowered by this duty, Marvel can make retcons to Spider-Man's continuity. Barring a mass exodus of readers from Marvel's version of Spider-Man's 616 universe continuity, it is the official version.
If I stopped reading Spider-Man at OMD, I would have an understanding of Spider-Man's continuity up to that point, and that might be complete and satisfying for me. And I could tell people that, and they would understand and accept that. It's my choice what to believe as a reader.
But if I start telling people that my understanding is the one true understanding and theirs is wrong, they would rightfully laugh at me, because it is commonly accepted by all reasonable people that Marvel's continuity is the official one.
So as you can see, comic book continuity in practice is a complicated thing that your definition is not adequate to describe.
I'll give you an example.
Marvel published a GI Joe comic book in the eighties. Written by Larry Hama, this book was beloved by a lot of people, myself included, and ran 155 issues. Around 2000, Image and Devil's Due began publishing a new GI Joe series. This series, called originally G.I. Joe Reinstated, and running through several different versions over the next ten years or so. This series purported to continue the story from Marvel's series, and this was accepted by most readers, and so it was true.
Then, a few years ago, IDW got the license for GI Joe, and decided to reboot it. A new continuity was started, which people recognized as separate from the Marvel/Image one, just as they recognize the Marvel one as separate from the various cartoons or the movies. Then, complicating matters further, IDW created a new series called G.I. Joe: Real American Hero, which brings back Larry Hama (who wrote every episode of the old series) and picks up at issue #155.5, immediately following the Marvel series. It retcons the entire Image portion of the continuity.
It's also a better book than the Image book, written by the same writer as the old Marvel series, and provides a better continuation of that continuity. And so, it is readily accepted by readers as such, because it is the best viable option for people who wish to continue reading stories set in that continuity. For someone like myself, who enjoyed/s all three series, I am perfectly capable of accepting this, enjoying all three series, and reconciling all of this within my mind without resorting to declaring that each one created a new set of characters and thus invalidating the very thing I'm seeking, a continuation of stories starring particular characters in a particular universe.
This is only possible because I and the other people reading these books, the readers, the audience, collectively agree that is true. Otherwise, the whole thing falls apart. All three companies could publish books, and people could read them, but there could be no continuity in any sense that comic book fandom as a whole perceives it.
It's not perfect, but life isn't fucking perfect.
And this is not life. It's fucking comic books. It's like a zillion times less important than most other things in the grand scheme of things.
You are entitled to your rigid definition and hardline attitude about what continuity means to you personally, but to suggest that you and a few like-minded individuals are right while everyone else is wrong is silly and arrogant, and opens you up to the kind of ridicule you are apparently treated with all over the internet and which you wear as a badge of honor which is itself a defense mechanism.
I have a very clear, sober, and rational grasp of this entire clusterfuck.