That's great, Lighter! That definitely ties together -at some historical point - "Shenandoah" and "Blow, Boys, Blow" with "Sally" some sort. Hugill does have a "Sing, Sally O!" which is aka "Mudder Dinah" on pp. 388-389. This shows up in Bullen, Colcord and Sharp as well.

Here is "Shallow Brown" Part 7

Colcord gives Captain John Robinson's version of "Shallow Brown" with the following note from Robinson:

"I remember hearing it ["Shallow Brown"] sung by the black crew of an American full-rigged ship, the "Garnet," of New York, at Macabei [Macabi], a guano island in the South Pacific [off the coast of Peru]. It sounded very musical coming across the still water, while to its accompaniment the captain's gig was pulled up to its place." (p. 57).

Here is an early accounting of the guano trade from 1866, which specifically mentions Macabi:

http://books.google.com/books?id=BzLOAAAAMAAJ&pg=PA581&lpg=PA581&dq=guano+trade+Macabi&source=bl&ots=i9EzuEv_sR&sig=hjr-yGfOmYJs

And one on the history of this trade:

http://www1.american.edu/ted/guano.htm

Unfortunately, they are not helpful in dating Robinson's experience. He went to see in 1859, but could have had this experience any time in the next thirty years at least. I have searched for the "American full-rigged ship, Garnet" but there were a number of "Garnets" and I haven't been able to put one at Macabi Island. It's too bad, because otherwise this is such a precise notation!

I would note that W.B. Whall's version of "Challo Brown" is very similar to that of Robinson. Whall was at sea from 1861-1872, so there is definitely overlap for these two men. However, if I'm not mistaken, Whall was on the other side of the world. They share the verse about "being a bright mulatto from Cincinnati," as well as the verse about "getting my clothes in order and sailing across the border." Unfortunately none of this really helps us date either Whall or Robinson, two of our earlier sailors. It doesn't help that Robinson published his collection in 1917 and Whall in 1910. Terry's version, published in 1926, seems to draw from both the Robinson and Whall versions.   

However, the Robinson version shares its first two verses with that published by Henry Alden in HARPER'S NEW MONTHLY MAGAZINE in 1882, here:

http://books.google.com/books?id=SsoaAAAAYAAJ&pg=PA282&dq=%22Shallow+Brown%22&lr=&cd=99#v=onepage&q=%22Shallow%20Brown%22&f=fals