Hope this helps:
Although this tune is very much in the style of Duke Ellington there is,in fact, no Ellington work called "Harlem Nocturne". What he is thinking of is a minor key tune that was recorded by many people,but grew to some fame as the theme song of Johnny Otis.
This info is from the Tom Lord Jazz discography,the final word and definitive study of Jazz recordings.
I never saw Ellington, but I'm told by a friend who has seen him that the song was a staple in Duke's live set for quite a few years. That probably accounts for why the song is so strongly associated with Duke, even though it was written by Earle Hagan. AFAIK, Duke never recorded it.
BTW, If you'd like to hear a mind bending rendition of the song, try Danny Gatton's transcription for electric guitar. That might be my single favorite cover song ever.
In various group formats Duke Ellington recorded the following titles containing the word Harlem:
Echoes Of Harlem
Boys From Harlem
Drop Me Off in Harlem
Harmony In Harlem
Jungle Nights in Harlem
These are the ones I know of, there may be more. Most of the tunes are available on the Mosaic box set "Complete 1936-1940 Variety, Vocalion and Okeh Small Group Sessions". I suspect they are also available on any number of Ellington compilation recordings.
223 recorded versions from 1940 to 2010.
For the ultimate tribute to Harlem,check out the work he simply called,"Harlem".Duke recorded it several times,notably with a large orchestra added to his band on the "Symphonic Ellington" on Reprise and several live versions recorded in Europe and issued on Pablo.