The Libby Backstory That Never Was
Here's the thing about Lost threads that went nowhere. The ones that went unresolved obviously had no bearing on the story. If you liked, and were satisfied by "The End"—as we were—then it doesn't really matter why Libby was in Hurley's hospital, what led her to cross paths with Desmond, etc. But then these things still beg the question...why include them in the first place?
True TV fans know that complaining about showrunners making things up on the fly isn't the felony it's made out to be. A good 75% of the plot developments on your favorite series were happy, serendipitous accidents and the Lost-imitators that have rigidly tried to map out a complete course in advance often stumbled in spite of it.
But the "making things up" argument gains weight when the fact that a Libby flashback never occurred proves that it never had relevance to the story and was simply there because the six-degrees-of-castaway-separation became something of an expectation.