Here is a real oddity, outtake, novelty tune that has a very unusual chord progression. Sour Milk Sea was written by George Harrison after their trip to India. Before they got to working on The White Album, they got together at George's estate in Esher and recorded demos of many songs that made the final cut. This one didn't for a few reasons, probably the main one being that it was quite similar to Savoy Truffle. They had just started their own label, Apple, and gave it to Jackie Lomax for his album. Other early Apple artists included Badfinger, James Taylor, and Mary Hopkin. The Jackie Lomax version featured most of The Beatles (missing John), Eric Clapton and Nicky Hopkins (piano on many Rolling Stones songs). Here are 3 versions, the original Beatles' demo, Jackie Lomax's released version, and a homemade blend of George's demo vocals over the rhythm track from Jackie Lomax's version.
The challenge here is to figure out the chords, obviously. The clue is find the bass notes, forget about the key. PM me with answers, OK to post questions or suspicions here.