You're still not making sense.This:
If I had to guess, I'd say you mean this: That the PCs might encounter the ancient wyrm for legitimate reasons instead of just due to a failure of information.
Which is true, but misses the point, which isn't about the proper home of ancient wyrms but rather about the degree to which the world should be designed so that the players have a good time and don't all lose characters due to random ancient wyrms that pop out of unexpected places and kill them.
When people argue that an ancient wyrm shouldn't be living next door to the town as a sort of trap for the PCs to stumble into and die, the issue isn't the wyrm itself, its the dangerousness of the encounters the PCs are likely to get into due to the wyrm.
If you:
1. Put the ancient wyrm next to the town,
2. Inform the PCs of its presence and make sure they're adequately aware of the guarantee of death if they fight it, and
3. Engineer it so that if or when they have to go into the wyrm's territory they don't have to actually fight it if they play things right,
Then you've done basically the same thing as the guy who didn't put the wyrm there in the first place due to a desire not to screw over low level PCs who can't fight the wyrm.
Both of you are designing the game world such that the PCs will encounter level appropriate fights. You're just including the risk of a level inappropriate fight if the PCs so choose, and then telling the PCs not to so choose. Both worlds are equally engineered and the outcome is the same.
Of course, this could be completely non responsive, because I'm just guessing the meaning of your cryptic writings.