- [C D# F# G# B] should be [C E♭ G♭ A♭ B], which makes an A♭7♯9 chord, a pretty normal chord. If you want the root to be C, we can do a couple things. From [C E♭ G♭ B A♭], you could make a C°(maj7♭13), but that's pretty weird. With B as the root, it's [B D♯ F♯ G♯ C], making B6/♭9, which is also weird.
- [G A# B D#] should probably be [F♯♯ A♯ B D♯], forming B+maj7 (also written Bmaj7♯5, among other names). If you want G as the root, you can have an incomplete voicing of G+(♯9) [G B D♯ A♯], also weird. With E♭ as the root, [E♭ G B♭ C♭] gives E♭(♭13).
- [G A# C] should usually be [G B♭ C]. There are so many (mostly incompletely voiced) options for this chord, I'll just go through a bunch of the more reasonable ones really quick: Gadd11, A♭maj9, Cm7, C7, C7sus, E♭6, F9/11 (or Fsus2/4 or Fsus2sus4, lots of ways to write it), G♭(♭5♭9).
- [C D F A#] should be [C D F B♭]. C9sus jumps to mind, as does B♭add2. [E♭ B♭ D C] gives us a variety of rootless E♭13 voicings. Rootless Gm11 works pretty well. Rootless A♭maj13♯11 is nice (the dominant version works too).
- The main reason I'm able to write such concise symbols for each note is because I'm writing in one of many accepted naming conventions. The one I'm using stipulates that the first thing to do is (after picking a root) look for the highest natural extension.
Using [C-D-F-B♭] as an example, my highest extension is F, which is an 11th above C. So, this is some kind of an 11th chord.
Next, I find the quality of the 7th chord based off the root I chose. Here, it's C7 (though there's no 3rd or 5th, which I'll address soon. Pretend there's an E and a G), so now we've got a C11, since the C7 is dominant.
Finally, all other extensions. Here, I'm left with the D, which is the 9th. Since the 11th implies the 9th, I now know that this chord is C11.
But there's one problem. Dominant 11th chords are usually voiced without the 3rd. Here, I've got no 3rd and no 5th, so I know I can just label that 11th as the suspended 4th. Since the 5th gets omitted extremely often, I now have a 9th chord with a suspended 4th, hence: C9sus. I just recommend that you get into the habit of not naming things dominant 11ths, because certain people don't like that, but no one objects to 9sus in place of 11.
As a better example, take [A♭ C E♭ G♭ B♭]. Highest unaltered extension is the 7th, and we've got an A♭7 chord. Next, the B♮ is the ♯9, so the chord symbol is A♭7♯9.
The reason we need the highest unaltered extension is because we don't want to have altered extensions right next to the root note (otherwise, is C♭9 a dominant C♭ chord or a C7 with a ♭9?).
I also try to avoid using "add" and "no" as much as possible. If the 5th is left out, I usually don't mention it, and if the 9th is left out but the 13th is there, I use parentheses to point out that the note doesn't imply any other extension (e.g. "Am7(13)" instead of "Am7add13"). Also, most people shorten "min" to "m", and "dom" to nothing at all. And in most cases, "2" should be "9", so avoid "sus2".