That's The Blues Old Man is for me Johnny Hodges' top soprano recording, so glad to see it included.
Ellington's first great soprano player was Bechet in 1924/5, although there are no recordings of that period. After Bechet left, Ellington found he needed both a clarinetist (Barney Bigard) and a sax player (Hodges) to fill Bechet's role. Hodges had taken some informal lessons on soprano from Bechet and the influence is evident in his soaring phrases and vibrato (as it is on alto as well). Ellington began featuring Hodges more and more on alto until after about 1940 Hodges pretty well stopped using soprano. The Ellington small groups that do feature Hodges on soprano are mostly from around 1938 -40.
There may be something in that, but the sources I have looked at are along the lines I wrote. Wikipedia says he was forced to give up soprano in 1946, although no reasons are given. Other sources confirm 1940 and give the impression it was his own choice. If it was over doubling fees, one might wonder why other Ellingtonians put up with it - Jimmy Hamilton (clarinet/tenor), Harry Carney (bari/bass clarinet), Russell Procope (alto/clarinet)...
It has been suggested that Duke wanted to reunite Hodges with soprano for part of his New Orleans Suite, but Hodges died before the recording of the whole suite was completed. It's poignant that the section Blues for New Orleans was both Hodges' last recording and one of his greatest blues performances on alto.
My favorite recording of Johnny Hodges on soprano is "Blue Reverie" recorded at Benny Goodman's Carnegie Hall concert in 1938 with members of the Ellington Orchestra, i.e. Harry Carney on baritone, Cooty Williams on Trumpet and of course Hodges himself, with Count Basie on piano, I think. I don't think I have the membership status to post links, but you will find it immediately on Youtube if you search for: Johnny Hodges, soprano, Benny Goodman, Blue Reverie. Happy to know what others think of this recording. It would probably be one of my "desert island discs"!