After some further and deeper research, I redact my last statements, it seems it may be true news, I have since found other sheet music for an alternative version of Oh Good Ale, and it seems that it is more similar to SCUMM BAR, when both sheet music is compared.
So the plot thickens, and it may be borrowed from a modal version of the tune.
You can listen to it here sung by British man Ernest Butcher on a 1916 vinyl
I have also contacted the fiddle player from “The Virginia Company” and he can confirm that the music was sourced from the original 18th century piece
SECRET OF MONKEY ISLAND FINALLY UNCOVERED! MICHAEL LAND SUED, TRIALED AND KEELHAULED BY 19th CENTURY BUCKANEERS!
No mistery then. Aaaw. 
I’m so relieved my aural skills didn’t fail in the end 
. And with the latest statement, we could be facing even a music from the real golden age of piracy (maybe).
“Would I be correct in saying that you guys borrowed the music from the game?”
lol super cheeky
“ it was sung by the clown, Joseph Grimaldi, about the end of the 19th century.”
or the grand-grand-son of one of these jokers?
That’s interesting! Though the song is from the right era, so it makes sense to play it in the Scumm Bar.
As we know, it’s not the only song that Land borrowed, seeing the bones song in MI 2 (apparently inspired by Dry Bones by the Delta Rhythm Boys).
The Amiga version that is. The PC version added those few extra notes at the end.
A little, but he had to be put in his place if he was the stealer. =)
Ron Gilbert realising the song he wants to use for the SCUMM Bar is pre-copyright:
shucks this is really cool.
I also like the fact that this music has a much longer history. It lends a certain authenticity to the game that we might have all picked up on subconsciously.
And why not? 
For example The Dig is using some classical music …
I’m selling these fine sheet music sheets…
Michael Land is credited for “original music” as far as I remember, so I think this acknowledges that there’s some “borrowed” (not written for the game) music as well.
Some of the themes might be “borrowed” but it may or may not have been intentional. There’s so much music floating around in a composer’s subconscious that a melody or two can seep in without realizing it’s from something else.
It’s hard to write something that is 100% original.
I guess the secret is to write music that can be reminiscent of other songs, but not a direct rip off.
That can happen. As a musician myself I ripped off unknowingly riffs from at least 3 songs (thankfully one was caught before recording) including one from a band I don’t even like, so yeah. But this theme seems just like an intentional take on a popular period song, which is fine. In the first “Pirates!” game I think all music was lifted from classical composers.
Thankfully it’s old enough that modern copyright laws don’t touch it - public domain!
Awesome pirating
I think Michael Land is probably disappointed in our collective lack of musical knowledge that it took us this long to notice what was, for him, probably a really obvious and appropriate reference 
