Formal structure of [142] "Back in the USSR":
          Intro   0:00-0:16
                    sfx    0:00-0:09
                    beat  0:09-0:16

          Verse 1  0:16-0:30
          Chorus   0:30-0:40

          Verse 2  0:40-0:53
          Chorus (ext)   0:53-1:06
          Middle 8    1:06-1:23

          Solo (v)    1:23-1:36
          Chorus   1:36-1:46
          Middle 8   1:46-2:03

          Verse 3   2:03-2:17
          Chorus    2:17-2:27
          Coda (m8)  2:27-2:43

Comments: The second chorus is extended by repeating the words "back in the US" twice before completing the phrase ("back in the USSR"). This elongates the duration of the chorus by three seconds (13 seconds, compared to the 10 seconds of the other four choruses).

Given that the solo functions as a verse (the solo instrument replaces the lead vocal, but everything else remains the same as heard in the verses), the macro-scale formal design can be seen as four iterations of verse + chorus + middle 8, with the first such iteration omitting the middle 8:

Lastly, in following this pattern of verse, chorus, middle 8, the coda is based on the middle 8, which is quite rare in Beatles music - something only used twice before in [15] "All My Loving", and [67] "In My Life".

[121] "The Inner Light"
The middle 8 is used twice, lasting 8 or 9 measures and 23 or 18 seconds each time (the second iteration transitions to the coda, accounting for the slightly shortened duration), totaling 26.3% (41/156) of the song's duration.

[122] "Lady Madonna"
The middle 8 is used thrice (with the middle of those three replacing vocals with a saxophone solo), lasting 8 measures and 18 or 17 seconds each time, totaling 38.7% (53/137) of the song's duration. The middle 8s also modulate from A Major to C Major.

[123] "Across the Universe"
"Across the Universe" is the 46th Beatles original not to use a middle 8. Instead, the chorus serves as contrast to the verses.

[124] "Hey Bulldog"
"Hey Bulldog" is the 47th Beatles original not to use a middle 8. Instead, the chorus serves as contrast to the verses.

[125] "Revolution 1"
"Revolution 1" is the 48th Beatles original not to use a middle 8. Instead, the chorus serves as contrast to the verses.

[126] "Don't Pass Me By"
"Don't Pass Me By" is the 49th Beatles original not to use a middle 8. Instead, the chorus serves as contrast to the verses.

[127] "Revolution 9"
"Revolution 9" is the 50th Beatles original not to use a middle 8. Instead, the chorus serves as contrast to the verses.

[128] "Blackbird"
The middle 8 is used twice, lasting 4.5 measures and 11.5 seconds each time, totaling 16.7% of the song's duration.

[129] "Everybody's Got Something to Hide Except for Me and My Monkey"
"Everybody's Got Something to Hide Except for Me and My Monkey" is the 51st Beatles original not to use a middle 8. Instead, the chorus serves as contrast to the verses.

[130] "Good Night"
The middle 8 is used thrice, lasting 4 measures and 14 or 15 seconds each time, totaling 22.3% of the song's duration.

[131] "Ob-La-Di Ob-La-Da"
The middle 8 is used twice, lasting 8 measures and 15 seconds both times, totaling 16.0% of the song's duration. The middle 8 tonicizes IV.

[132] "Revolution"
"Revolution" is the 52nd Beatles original not to use a middle 8. Instead, the chorus serves as contrast to the verses.

[133] "Cry Baby Cry"
"Cry Baby Cry" is the 53rd Beatles original not to use a middle 8. Instead, the chorus serves as contrast to the verses.

[134] "Helter Skelter"
"Helter Skelter" is the 54th Beatles original not to use a middle 8. Instead, the chorus serves as contrast to the verses.

[135] "Sexy Sadie"
The middle 8 is used twice, lasting 5.5 measures and averaging 11.5 seconds each time, totaling 11.9% of the song's duration.

[136] "While My Guitar Gently Weeps"
The middle 8 is used twice, lasting 16 measures and 34 seconds each time, totaling 23.69% of the song's duration. The middle 8 modulates from A minor to A major.

[137] "Hey Jude"
The middle 8 is used twice, lasting 11.5 measures and 37.5 seconds each time, totaling 17.5% of the song's duration.

[138] "Mother Nature's Son"
The middle 8 is used twice, lasting 7.5 measures and 21 seconds each time, totaling 25.1% of the song's duration.

[139] "Yer Blues"
The middle 8 is used thrice, lasting 4 measures and averaging about 10 seconds each, totaling 12.1% (29/239) of the song's duration.

[140] "Rocky Raccoon"
The middle 8 is used twice, lasting 8 measures the first time and 9 measures the second (because the second middle 8 concludes the song), averaging 24 seconds each, which totals 22.6% (48/212) of the song's duration.

[141] "Wild Honey Pie"
"Wild Honey Pie" is the 55th Beatles song not to use a middle 8. The novel structure of the song has no need for a middle 8.

[142] "Back in the USSR"
The middle 8 is used twice, lasting 10 measures and 17 seconds each time, totaling 14.7% (24/163) of the song's duration.

[143] "Dear Prudence"
The middle 8 is used once, lasting 5.5 measures and 17 seconds, totaling 7.2% (17/235) of the song's duration.

[144] "Glass Onion"
The middle 8 is used once, lasting 10 measures and 19 seconds, totaling 13.9% (19/137) of the song's duration. This middle 8 concludes with two bars borrowed from the end of verse B.

[145] "I Will"
The middle 8 is used once, lasting 8 measures and 19 seconds, totaling 18.1% (19/105) of the song's duration.

[146] "Birthday"
The middle 8 is used twice, lasting 10 measures and 14 seconds each time, totaling 17.3% (28/162) of the song's duration. The middle 8 modulates form A major to C major.

[147] "Piggies"
The middle 8 is used once, lasting 7 measures and 18 seconds, totaling 14.6% (18/123) of the song's duration.

[148] "Happiness is a Warm Gun"
"Happiness is a Warm Gun" is the 56th Beatles song not to use a middle 8. The novel structure of the song has no need for a middle 8.

[149] "Honey Pie"
The middle 8 is used twice, lasting 8 measures and 13 seconds each time, totaling 16.3% (26/160) of the song's duration.

[150] "Savoy Truffle"
The middle 8 is used twice, lasting 8 measures and averaging 15.5 seconds, totaling 21.1% (31/174) of the song's duration.

[151] "Martha My Dear"
The middle 8 is used twice, with the first iteration incorporating a substantial extension. The first middle 8 (extension included) is 15.5 measures and 42 seconds long; the second is 8.5 measures and 23 seconds long. Combine these two, and the middle 8 totals 43.9% (65/148) of the song's duration.

[152] "Long Long Long"
The middle 8 is used once, lasting 7.5 measures and 26 seconds, totaling 14.1% (26/185) of the song's duration.

[153] "I'm So Tired"
"I'm So Tired" is the 57th Beatles song not to use a middle 8. Instead, the chorus serves as a contrast to the verses.

[154] "The Continuing Story of Bungalow Bill"
"The Continuing Story of Bungalow Bill" is the 58th Beatles song not to use a middle 8. Instead, the chorus serves as a contrast to the verses.

[155] "Why Don't We Do It In The Road"
"Why Don't We Do It In The Road" is the 59th Beatles song not to use a middle 8. (There is no contrast to the verses, with the possible exception of the percussion introduction).

[156] "Julia"
The middle 8 is used once, lasting 5 measures and 18 seconds, totaling 10.2% (18/176) of the song's duration.


Updated cumulative chart:

"Yesterday" features strikingly similar chord progressions with Ray Charles' 1960 cover of Hoagy Carmichael's “Georgia on My Mind". These similarities, however, are not terribly easy to hear. They are much more easily understood visually, hence the example below (click it to enlarge), which displays "Georgia on top with "Yesterday" on the bottom, each with chords with red lines denoting similarities between the  progressions.

Of the 11 different chords used in the verses of “Georgia on My Mind”, all but one corresponds to a comparable – if not identical – chord in the verses from “Yesterday”.

Attempting to prove Paul's awareness of Ray Charles' recording of “Georgia on My Mind” prior to the composition of “Yesterday” would be utterly futile, but it does seem extremely probable that Paul knew of the song because he uses that title phrase in his lyrics to “Back in the USSR”.