It's the story within the book. It's the story of how Salinger became a writer, the choice to be that, how that happened, the voice that permitted it. That's his main choice, and the other things follow, the talent put to use, the work itself, the details of a story. There's the embryonic quality to the early works, and a preservation of that in later ones. Holden is the ontogenic.
That's the story I think every real artist of note has to tell: why did I become what I did, in my own form of the ideal. It would also include the discovery of the ability to write, or paint or sing (intuitively understood.)
For many reasons Salinger was a searcher, before, during and the long remainder of life. I know the type. The writer would gravitate toward sacred texts, but places himself close to the same level as far as the possibilities of what he's saying, either cloaked or less so. Or he tries to absorb them.
The women in Salinger's life, wise creatures that they are, would see the pattern. He tries this, he's a Buddhist, then a Zen Buddhist, and then a Hindu Vedantic, while importantly keeping a character in a Jesus Prayer mantra. He eats thawed frozen peas for breakfast, puts on his overalls, goes to his writing 'bunker,' works away, comes back, watches Lawrence Welk after dinner to dance with his lady. My how he shifts around, one might think. He's searching a lot, but he never lands on anything, but yet to his credit keeps on practicing, and hey, compared to the materialist values of the mainstream, there's a soothing aloe vera reality to him.
I'd put MacGowan in the same boat. A guy who can sing. So, he does it.