HylianAngel: Sigma: …because Toby didn’t complete them yet? Those rooms are numbered in order of completion. They’re not ordered by completion date, the rooms are ordered in the way they are encountered throughout the game, with only the Annoying Dog rooms being out of order. Toby purposely chose to have the rooms numbered in this specific order.

https://www.reddit.com/r/Underminers/comments/3wqqez/i_believe_ive_solved_gaster/

That very link seems to indicate otherwise, dude. For the most part, he seems to have also developed most of the rooms in order, giving off the impression you got.

HylianAngel: Sigma: So how the hell could you think that his true form is that of a character who can be encountered on every route? Because “fun” events about Gaster can occur upon any route. Why would Gaster be restricted to a specific route? And whatever the case may be, it’s just a fun and inconsequential idea. Whether or not Gaster is the Annoying Dog or not, it doesn’t affect anything important. There’s no reason to be upset over it.

*encountered normally

I meant to imply that it’d be ridiculous to think that Gaster is a character that you can encounter on every single run just by progressing through the game. It makes more sense to think that he’s an obscure character that you have to work hard/get lucky to find.

Let’s not forget that the Annoying Dog (which is his actual name) is the embodiment of Toby Fox within the game. Do you really think he would give himself such an important role as to also be a former scientist who’s essentially responsible for the survival of monster kind? Don’t you think that’d be conceited? (if that is the right word…) All of the actions of the Annoying Dog have been silly and trollish in nature. He just annoys various people, including the player, within the game with his wacky antics. Sure he absorbed the artifact, and THAT might be important, but that still falls in line with his entire character. Does it make any sense for this kind of character to work seriously alongside Asgore and create a core?

And before you pull the Sans card, he very well demonstrates in the game that there’s more to him than meets the eye. Whereas the Annoying Dog (not White Dog) does not.

Also regarding your second point, The River Person, the Wrong Number Song caller, and Sans never use Gaster’s name either. The “It’s never officially stated” card goes both ways. As for his followers, you were right about them not directly stating that Gaster no longer exists. However, I’d like to point out how out of place they are compared to the other NPCs, as well as the fact that they all vanish after being spoken to. The Gray Kid directly speaks about not existing. Though he/she doesn’t mention Gaster directly, it could be inferred that they were speaking about him due to their sharing the monochromatic nature with the others.

Though I admit the Gray Kid might’ve been talking about someone else, I still like to imagine that all four monochromatic NPCs were somehow involved in/caught in the crossfire of the same accident.

legotrekker: Sigma why are you upset about this dude?

I wouldn’t say I’m upset really…