I have no idea what Joybell, or Joe, have in mind about limits on the Carter songs. Only pre-1941? Perhaps they will comment.

"Beautiful Isle O'er the Sea" is a composite of three (four? see last paragraph) songs: "Beautiful Light O'er the Sea, There's someone waiting for me," in Belden, which also has elements of "The Prisoner's Song"- and the 'will not marry' verses found in songs related to "Paper of Pins" and in many folk collections. This is a problem with a number of Carter songs- 'Mix and match'. Of course this was a common folk practice.
Belden printed the song in 1940, collected from a MS ballad book compiled by Ada Belle Cowden, date not stated.
(I found myself fitting the words in Belden to "Beautiful Brown Eyes," and "The Prisoner's Song," a new earworm to try and get rid of).

"Beautiful Isle of the Sea" was a song by George Cooper with music by John R. Thomas, 1865; sheet music published by Pond (at American Memory). Not close enough to the Carter song, but here is the chorus:

Fountain of pleasures untold,
Beautiful isle of the sea!
Fountain of pleasures untold,
Bautiful, beautiful isle of the sea.
(Also issued as a song sheet by Johnson)