Formal structure of  "Lady Madonna":
Intro (v) 0:00-0:09 A major
Verse 1 0:09-0:18 A major
Verse 2 0:18-0:26 A major
Middle 8 0:26-0:40 C major
Tag 0:40-0:44 transitional (tonality ambiguous)
Verse 3 0:44-0:53 A major
Break (v) 0:53-1:01 A major
Solo (M8) 1:01-1:15 C major
Tag 1:15-1:19 transitional (tonality ambiguous)
Verse 4 1:19-1:28 A major
Break (v) 1:28-1:37 A major
Middle 8 1:37-1:50 C major
Tag 1:50-1:54 transitional (tonality ambiguous)
Verse 5 1:54-2:06 A major
Coda (v) 2:06-2:17 A major
Comments: This analysis incorporates a new structural label: the tag, a brief but distinctive musical motive that could be interpreted as an extension whatever section preceded it, but is different enough to warrant independent formal designation.
A tag is rather similar to a bridge in that a formal analysis on the briefest level would not distinguish a bridge or tag, but on a more detailed scale, analysis would make such a distinction. Also, tags are often transitional and cohesive in nature. Examples of tags in Beatles music would be the guitar motives in "Day Tripper", and "In My Life", among others. At some point, I will revise my earlier analyses of those songs.
With that in mind, looking specifically at "Lady Madonna" we can see that at least in this instance the tag also functions as a tonally transitional element - the tag connects the middle 8s (in C major) with the verses (in A major). As a result, the tag's tonality is a little bit of both C and A major.
This blog is a workshop for developing my analyses of The Beatles' music.