Thanks, Michael,
The sound of this nocturne is certainly familiar to me, although I don't believe it's played as often as many of the others in the set. I have two editions here, the Paderewski and also Kalmus, and both end at Op. 72, No. 1. It appears in neither, so it was a bit confusing. You perhaps have the Henle edition there?
My sense is that, right or wrong, there is sometimes a prejudice concerning posthumous works, i.e., "If the composer had wanted a certain piece published, he would have submitted it in his lifetime!" For example, some artists will play the first seven Chopin Polonaises, but omit all the posthumous ones. The same, believe it or not, with the Fantasy Impromptu when the Impromptus are recorded. Often there must surely have been extenuating circumstances as to why a composer might have been enthusiastic about his intention to publish a work--but for whatever reasons it just never happened. Likewise, some composers doubtlessly hid scores away having qualms about quality. I doubt that the posthumous publishing of Ravel's "Seranade grotesque" does him much credit. Similarly, there is Rachmaninoff's Etude Tableau, Op. 33 No. 3 as we now know it. He had integrated that music into the 4th Concerto, so kept the etude under wraps, not wishing to publish it and thus repeat himself in his scores. In one way, it's nice to have that etude now; but somehow, I don't think he'd be pleased knowing that it was published in 1950 causing that dreaded duplication in his ouvre. So I guess each posthumous work has its own story to tell, good or bad.
I don't want to digress more, as this is Kylie's posting. I like to help by commenting, but where I am not too familiar with this nocturne and don't have a score here, I'd best let others give feedback.