The ii-V-I progression was used as the foundation of thousands of show tunes from Broadway and Hollywood and in jazz originals. By the early 1950's, when this tune was written, this cliche was almost entirely juiced, squeezed of its musical meaning. A groove by that time had been worn so deeply into listener's brains that a composer could use this expectation to generate suprise by intentionally jumping out of these tracks to land on a new harmonic destination.
	The game in Four is to set up the sound of Eb Major very strongly using a EbMA7 chord repeated twice, then a number of times set up the ii-V portion of the ii-V-I cliche in different keys to make it seem that it would take us outside of Eb Major but then always slide into a sensible sounding chord that is different than the I chord that would be expected to finish the cliche. The unexpected chords that take the place of the expected I chords, Fmi7 and Gmi7, are all in Eb Major and serve as aliases of the EbMA7 chord.
	This progression is like a fast drive through Eb Major with loose steering that points us off in the direction of other keys which we quickly correct and aim back down the path of Eb Major.
	The ii-V sequences that were chosen for the feints into the alternate keys, were Abmi7-Db7 and F#mi7 B7. When the feint is towards Abmi7-Db7 the unexpected resolution is Gmi7. When we feint towards F#mi7-B7, the correction is Fmi7. These are arranged so that we hear a downward sliding ramp of mi7 chords (Abmi7-Gmi7-F#mi7-Fmi7) in the middle of sections and a shorter downsliding ramp (Gmi7-F#mi7-Fmi7) as we approach the end of each section.
	These slides by mi7 are unexpected and really catch your ear.
	When we play the second 16 bar section of the tune, the shorter downslide of the mi7 chords (Gmi7-F#mi7-Fmi7) occurs twice as fast as it happens the first time through the sequence in the interest of increasing the speed of harmonic motion at the end of the form.
	In many of the places the Fmi7 and Gmi7 chords occur you could substitute EbMA7 instead. There are versions published in different fakebooks that notate the changes in this manner. This causes the downward slide of mi7 chords to be notaionally obscured, and blurs the slide feeling somewhat, but the sliding effect is still audible.