It’s difficult to distinguish between chromaticism and modal interchange sometimes, I guess it’s a grey area where they, as you say, look different depending on your perspective.

Still, from my observation, I think holding to a cohesive modality in the first section, is a bit more complex than what the organic flow warrants. I only see two key’s present in the song, with some descending chromaticism in the bass line. Namely, A min (Aeolian) and G major. It should be noted that these keys differ only by an F# in G Major, whereas F is natural in A min. I also don’t look at the intro as a series of chords, as much as an evolving harmonic center. The melody starts on an A minor chord, and in three steps (chord 3 for your purposes) evolves into a C major/G. It gets there through a chromatically descending baseline, which is an independent theme from the underlying A minor or C major harmony being droned underneath the bass and melody. Additionally the melody on the high E string is initially an ascending melody contrasted against the descending bass line. Part of why this is so organic, is because of the relationship between an A minor triad and C Major/G. They are relative chords, each sharing two notes in common (A,C,E – C, E, G). The baseline provides a leading tone progression from (G#) that offers pleasant resolve to the relative major. Following that the chromatic descending bassline on the Cmajor/G, the chromaticism descends yet again a half-step to F#. F# is used to briefly introduce some tonal ambiguity by being played under a D Major, a theme which is reinforced and embellished throughout the song as pivot between Gmajor and Aminor.Cmajor. Lastly the bass line descends a fifth-half-step, to F natural returning to A minor. The resolve on A minor for this section of the song can be seen in two lights. First it is a relative chord to FMajor 7, the preceding chord (F, A, C, E – A, C, E). Additionally, while not the lowest note in pitch, the Aminor played in open position contains the sixth-half-step from the dominant baseline, E (played on the 4th string in open position).
This trend continues throughout the song, in an embellished way, but given the half-step chromaticism, I think it makes more sense to view the song as a harmonic tension between Cmajor/Aminor and Gmajor, rather than independent chord modulating through different keys. In other words, the bass-line is fluid rather than static, and entitled to occasional harmonic deviations within a centered key. Just my perspective.

N

I think that’s one of the points you were getting at isn’t it, when you say it avoids those notes yeah?