Watch the Extreme Substitution Example online guitar lesson by Frank Potenza from Jazz Harmony Handbook
An extended backcycling sequence in bars 1-4 opens this version. In bars 9-10, we have a II/V followed immediately by its sub II/V (Gm7/C7/Dbm7/Gb7). In bar 6, we see Bm7/E7, which is a slightly different way to approach bar 7 than we've encountered thus far. Having the ability to hear and identify these variations when they're being used is critical. Ear training should be a lifelong endeavor for the serious student of music.