These two are notable for using, despite the pro minstrel singing style, idiomatic blues lyrics that were around in folk blues tradition:

"Nigger Blues" George O'Connor 7/16
https://www.youtube.com/watch?v=ZrgEZN1hj6w

"Dallas Blues" Marie Cahill 1/17
http://www.loc.gov/jukebox/recordings/detail/id/4660/


This is interesting because it's blues guitar:

"Palakiko Blues" Helen Louise and Frank Ferera 1/17
https://www.youtube.com/watch?v=TfMbIBajMyU

Helen Louise died in 1919. Some more early recordings of blues guitar:

"Chain Gang Blues" Sam Moore 7/21
https://www.youtube.com/watch?v=Aja76WQsU8c

"Teasing The Frets" Nick Lucas 7/22
https://www.youtube.com/watch?v=BMQ_Cu4S7ik