Well said, Steve.

The themes are similar, but they're hardly the "same song." Anybody hearing one and knowing the other would most likely say, "Hey! I know another song that's like that!"

Not "I know that song!"

Yarmouth is relevant only because Sam Larner sang about it in a forebitter that Bellamy was familiar with, suggesting (along with all the evidence) that he (or someone) thought it was a good location for salty adventures.

But that's total conjecture, of course, and it would be meaningless of "Yarmouth Town" had thoroughly traditional antecedents.

But it doesn't.