Put a little more thought into it and you would realize your last sentence is just plain absurd.
As a rule, I like to put just the
right amount of thinking into what I write. It's a bit like cooking. Too much results in a burnt lump!
A fictional character within the fictional environment of the game would not inherently have any knowledge of what your previous characters did.
On the other hand, any fictional character I create has me as their author. They know whatever I decide they know. As fictional characters, they are ultimately shaped by all the previous experiences I've had gaming & otherwise; all the books I've read read, film and television I've seen. All the genre assumptions that come of that. That's what they're
made out of.
You may not agree with all that, but it does have the advantage of being true.
Nor would they have previous detailed knowledge from the monster manual of all creatures likely to show up nor their number of hit points and special abilities.
Gamers are going to learn the games they play. Short of reading the current published module I'm running, I'm cool with acknowledging the fact experienced players are, in fact, experienced. If I want to confound, challenge, and/or surprise them, all I need do is make their assumptions work against them by customizing things a bit.
Your own definition specifically includes regards to one's previous play experience by the two elements inherently being a "fictional character" and the "game's fiction" as both elements naturally create a set of bounds within which you are expected to choose your actions.
Nothing in my description said anything about "natural bounds". I'm guessing if I were to use that phrase, I'd mean something significantly different than you.
If you have a character act on knowledge of these things that the fictional character within the fictional environment would not have knowledge of, then you are not taking on the role of a fictional character within the rules of the fictional environment.
If by this you mean something like plain old cheating, i.e. reading the current module to gain an advantage, then yes, I'd agree that's poor form. But outside of that? The whole game is built around having & using outside knowledge. We model PCs after characters in external media. We let genre- and adventure-writing conventions guide our in-character decision making. Character decisions are often shaped by consideration for the other real people at the table, i.e. metagaming in service of the social contract. In most systems we're forced into acquiring some level of system mastery in order to get things done. Most settings can be described as a thin crust of specific custom-written fiction layered over a much larger mantle & core made of shared assumptions/elements derived from various external media (game-related & otherwise).
You may as well simply be playing an electronic game with the game guide revealing all the games secrets open at your side and all the game cheats activated.
If all we're talking about is outright, egregious cheating, then yes, I agree.