Son House's Death Letter Blues

[Patrick Dionne]

Hello. I am currently putting together a multimedia analysis of a
performance of Death Letter Blues by Son House.
Here is my problem:the version recorded in 1930 (My Black Mama Part 2)
differs from the versions recorded after 1960 in a few important respects.
In the 1930 version, there is no slide and the voice and the guitar accent
practically every syllable. Also, the song structure is the consacrated
A-A-B twelve bar form. However, upon his return in the sixties, House
played the song on slide, basically speeding up the accompaniment that he
used for other 16 bar songs. Furthermore, while retaining the 12 bar form,
he adopted an A-B-A-B strophe thereby cramming two lines in the first four
bars.
Can anyone explain to me why those changes occurred? Also, I know that
upon his rediscovery in 1964, Alan Wilson helped him remember and rehearse
his material. Are there any accounts of those moments?