Toei sure has their way with classification don't they? I feel like future Sentai series might repeat this same hiccup xD

Well, they seem to have things on track. They cleared up a few grey areas thanks to Gokai and made the classifications rather clear.
So unless we get another Black Knight, I don't think there will be another hiccup.
...I hope.

What about Kyoryuger's other rangers besides the core 7?

Kyoryu doesn't have a core 7.
Violet, Grey, Cyan, and Silver are all considered Additional Rangers, which is just how it sounds.

I would say that AbareKiller is the sixth. He had a mech that could form it's own gattai. That is pretty common among sixth rangers.

His overall demeanor is very much that of most sixth's.

Yes, but I wouldn't just say so because of Gokaiger. That wasn't an attempt to officially categorise everyone, just an anniversary series that pigeon holed characters into specific slots for the purposes of storytelling and convenience.

Otherwise you can use the same "official" categories to claim that KuwagaRaiger is a pink ranger.

No you couldn't. That's just being faecitious for the sake of it.

He was included in the lists with the pink keys and Aihm was typically the one to transform into him. My point was that too many people are over analysing Gokaiger, when everyone was just thrown into categories by the makers of that show for convenience, it wasn't meant as the word of god.

Kuwaga isn't pink, TimeFire isn't black and the only reason I can see why you'd count Abare Killer, but not Geki Wolf or Chopper is because there were two of them and they didn't want two characters from the same show (the Go-On Wings were basically treated as one and they did a whole thing with that, which wouldn't really have worked for Geki).

Some were thrown into categories. But I don't think anyone's going to look at Kuwaga and think "Oh he's a pink ranger" rather than "well he's there since Hurricaneger didn't have pink or (standard) green rangers". That's just common sense.

With the exception of including Gosei Knight (and even then I would say there's basis for argument) and maybe the exclusion of Geki Chopper/Violet, Gokaiger's list of sixths was pretty solid. Abarekiller ticks pretty much all of the boxes one would come to expect of a "sixth" ranger, and the show recognised that so I hardly see it as a reason not to take stock in it.