P.S. Howard Odum gave plenty of discussion of the knife playing by black guitarists that he encountered during the 1905-1908 period in his 1911 article. Odum happened to collect in Georgia and Mississippi because those were his two homes at the time. The 12-bar "Knife-Song" he described was similar to some of the music recorded during the '20s on by relatively old blues musicians, some of whom were playing before 1909.

For all we know, Odum may have first encountered slide guitar in 1905 or 1906, and Handy in 1906 or 1907.

Note that Handy said he had heard the song "Got No More Home Than A Dog" in about 1895, and note that one of the main differences between "Got No More Home Than A Dog" and the Tutwiler song (neither of which mentioned "blues" in their lyrics as reported by Handy, and both of which were 12-bar AAA) was... that presence of slide guitar itself. Had that singer Handy heard in about 1895 (Handy gave his name, Phil Jones) heard Hawaiian guitar as of about 1895? Likely not.

Here's part of Odum's 1911 discussion:

"Very much like the railroad-song is the knife-song, which has also
been described previously. Sometimes the two are combined; and
with the [imitation of the] blowing of the whistle [and] the ringing of the bell, and the ' talkin' ' of the knife as it goes back and forth over the strings, the ' music physicianer ' has a wonderful production. Many songs are sung to this music. One version of the well-known knife-song has been given. Another, which is sung more generally in the Southern States, follows. The verses consist of either a single line repeated, or a rhyming couplet. Two lines are sung in harmony with the running of the knife over the strings of the negro's guitar; while the refrain, ' Lawd, lawd, lawd! ' wherever found, is sung to the ' talking ' of the knife. The other two lines are sung to the picking of the guitar, as in ordinary cases."

(That use of the same simple refrain such as "Lawd, lawd, lawd" at the end of every stanza or many stanzas in a 12- or 16-bar song was favored by some of the musicians about Leadbelly's age, whether with slide or not.)