I've read every tutorial on artificial harmonics and they never seem to deal with the most direct issue regarding artificial harmonics. Since the node changes depending on the length of the string from the bridge to the fret you are pushing on, how do you prepare for artificial harmonics of notes/frets you haven't practiced yet? I mean I could get the artificial harmonic just right for a couple frets, but am I really supposed to practice every single fret and memorize exactly where to hit the string with the pick/thumb technique for that fret? That sounds ridiculous. How do you practice AHs to prepare yourself for using it more versatily than just the immediate fret you practice on? Are there certain spots that produce AHs much more often than others?
There are certain places on the string that contain more nodes than others.
For instance on my guitar the side of the neck pickup that's pointing toward the bridge will most often give me a harmonic. On the odd occasion that it doesn't; I just pick closer to the bridge until I get it and remember that position.
Gear List:
B.C. Rich NT Jr. V (With Seymour Duncan AHB-1 Blackout in bridge)
Electro-Harmonix Metal Muff
Marshall MG15DFX
Jazz III picks
DR strings
Planet Waves Cables
The positions of AH points on each string are actually based on natural harmonics. So, you have strong natural harmonics above: 3rd, 4th, 5th, 7th, 9th, 12th fret, and then it goes the same numbers just plus 12 frets (15th, 16th, etc.) Notice I say strong points because there is unlimited number of nodes, but most of them give too quiet harmonics to be of any use.
So, for every fretted note, you'll have an AH above that fret plus the fret number that NH appear on. So, for 8th fret, you'll have AH's over (8+3)th, (8+4)th, (8+5)th, (8+7)th fret, and so on, and so on...

Sure, when you pass the 24th fret, then continue with imaginary frets, so try to locate where, for example, the 32nd fret would be (if we're still talking about note on 8th fret).

There is an easy way to quickly find out harmonic spots on strings. lightly touch the string as you would when preforming NH, but then tremolo pick the string and continue moving your left hand finger upthe neck, still lighty touching the string. You'll notice that over certain frets you hear more than just dead notes, partly muted harmonics actually.
how do you prepare for artificial harmonics of notes/frets you haven't practiced yet?

Practice enough that you get a feel for it.

Basically, if you're aiming for a random squeal PH, generally having solid PH technique and just aiming nearish the bridge will do. For more specific tones you have to practice finding the exact point with speed and precision, although as you won't be looking, you just have to "feel it out" a lot of the time.

Very few players are aiming for specific nodes with pickstyle artificial harmonics.