Your comments on "Old Blue" piqued my curiosity. The earliest recording (and if not the earliest, one of the earliest) appears to be by Jim Jackson, who recorded it in February 1928 under the "old Dog Blue" title. Jackson seems to have claimed credit for it, though the song sounds like it goes back further than that. I actually have that recording, as it is on the rather wonderful 3-volume "Anthology of American Folk Music" compiled from old 78s by Harry Smith back in the early 1950s. For years, I had a cassette dub of the 3 original LPs plus a photocopy of the booklet. Then about 15 years agao, it came out as a CD box set - all 84 tracks.
Apparently Harry Smith planned a 4th volume which didn't come out at the time but there is also a CD issue of what that would have been, based on Smith's notes. In addition, there is a fan compilation of similar material, 4 CDs of about 100 tracks, none overlapping with the original 84 tracks.
If you have any interest whatsoever in American folk music or wonder where some of more recent music derives, these early commercial recordings are seminal stuff. Few are smooth and many may seem hard-going at first, but they repay repeated listening many times over. There's also a bit of education mixed with humour . Harry Smith sometimes provided telegrammatic newspaper-style headlines to summarixze songs.
For example, "King Kong Kitie Kitchie Ki-Me-O" was described thus: "Zoological Miscegny Achieved in Mouse-Frog Nuptials. Relatives Approve". Some may recognise this as the old song, "Mr. Froggie Went A-Courtin". Smith adds: "In the register of the London Company of Stationers for November 2, 1580, there is an entry titled, 'A Moste Strange Wedding of the Frogge and the Mouse'; probably the same song".
That may not be the best of examples on which to urge you to get this set. There are folk songs, there are country blues, dance tunes, gospel hymns, ballads about murders, comedy numbers, some jug band music, outlaw songs, string bands, Cajun recordings - and so much more. I tend to think of it as treasure chest but, if that is overstating it a bit, then it really is a treasure map.