Hello @agnes here’s a link for the harmonic analysis of days of wine and roses
Yes the Eb7 is the tritone substitution going to the VI , I m still learning and sometimes i am blocking on one chord too. A good way I find is to just ignoring it , and coming back after a while on it . Sometimes even simple things dont comes out at first sight . On this tune lot of subdominant 251 that can lose us. Thinking those transitory key , looking for 251 from different keys, often give us the solution .
In days of wine and roses in the first subdominant minor 251 (Am7 D7b9 Gm7) the IIm is not IImb5 can already confusing !! , Often instead of 7mb5 we could find minor7, instead of m7 a dominant 7, sometimes 7 becomes major . But the ears often are not surprised even the Theory is not respected . Another point is the we could have different analysis of the same chord progression from different people , which could be both right just different point of view .
Hope it could help