I don't think that what has been covered in discussion is when there is more than one accepted or more than one "genuine" interpretation or version of roughtly the same song, like "Lady from Armentiere". In order to use all of the verses of the song, or at least all of the one I've gleaned from the Mudcat and other sources, I'd have to sing for a half hour.
Also, musical ability (singing, instruments) should also be taken into account, at least in my case. I was not trained professionally in the use of my baritone ukelele, but from my uncle, who can hardly play either, but who has 1.)an endless supply of songs ranging from the above ballad to the Good-n-Plenty commercial of yesteryear, and 2.)rampant enthusiasm as songleader. Would E.Y. Harburg really mind that I shifted a verse in "Lydia the Tattooed Lady" in order for me to sing it adequately?
Yes, in the written form, the original words should be kept as closely as possible, but in performance, the circumstances should try and fit the intention, i.e. entertaining family and friends. To use an example, when Franz Lizst transposed Beethoven's 9th Symphony (Chorale) from full orchestra and chorus to a solo piano, I am sure he knew full well that a good bit of the drama, impact and small nuances of the work would be lost in moving to one solitary 88 keyed voice. But then, you'd have an opportunity to play the 9th in a dark, intimate lounge without resorting to the time, practice, and expense of a full-blown production and hiring a fat woman to take a solo.
I've heard both versions of the 9th, and while the staged one damn near brought me to tears, the piano recording I own has its merits as well. As should personalized versions of favorite songs.