Many chords don't have all strings playing at once though. It's definitely possible to play some 3 string chords on various places on the neck, with chromatically identical notes, but tonally different results. 6 note chords are of course much more easy. Lead lines however can be placed in a variety of ways, some of which lead to easier transitions to future chords, or whatever the case may be. To be able to identify the specifics on not a known guitar but rather an arbitrary guitar that might for instance have radically different pickups, or different strings, or may be in a variety of levels of "in-tune" all the way up the neck... I'd be surprised if this could be done accurately in real time - at least not with a standard mono-out from a guitar.
That's the benefit of using separated pick-ups, and an output that can encode that data in close to real time, so that instead of just trying to figure out "collection of notes = what?" you figure out "where is that note on that string", which could even be calibrated by playing an open chord and seeing what notes it gave for alt-tunings and capos...
But of course, I'll assume most games are just going to ignore alt-tunings and capos and half-capos, and bending, and harmonics, and false harmonics, and 7 and 8 string guitars...
Oh and as for unique notes, a 24 fret guitar will only have 48 unique semi-tones represented. as the tonal distance from the lowest open E to the highest open E is 24 semitones (two octaves). 48 unique semi-tones are mapped against the 144 unique fretting positions, and some notes repeat more than others, with the smaller 2 note intervals, appearing 3, 4 or 5 times on the fret board with nearly exactly the same hand position required, and 3 note chords appearing 2, 3, or 4 times.