I've got such beef with these kinds of 'grenres'. Young Adult and New Adult are targeted age ranges, not subjects. The subjects are things like 'coming of age' (for YA) mixed with whatever else - fantasy, paranormal, whatever.
So with that little bias on the table, where YA is essentially the years around puberty (think 13 - 17), and New Adult is just that: new adults (18 - 23 or so). Both have a lot of slice-of-life elements dealt with during those periods in life, which is why I said puberty and coming of age for YA. NA is less about 'discovering your identity' and more 'finding your way in this adult world'.
Does that help?
The Other Kind of Roommate - Like Fight Club meets X-Men meets The Matrix meets Superbad.
Raven Wilder
Wait, how do you distinguish "new adult fiction" (fiction for new adults) from "new adult fiction" (fiction for adults that is newly published)?
"It takes an idiot to do cool things, that's why it's cool" - Haruhara Haruko
This is a title.
Presumably there is no specific category stuff that's new, for adults. Stuff that's for adults is placed in the adults section, possibly at the top of the list because it's new. :P
You fell victim to one of the classic blunders!
![[up]](https://static.tvtropes.org/pmwiki/pub/smiles/arrow_up.png "[up]"){kind=icon}
Pretty much! We totally grown-up people don't need a special section, 'cause we're just so mature and get everything for being awesome. :D
It's never been a problem in practice to tell the two apart; it only just seems like it would be when you think about it too long.
The Other Kind of Roommate - Like Fight Club meets X-Men meets The Matrix meets Superbad.
I saw a Goodreads list on these, and didn't get what it was even after a cursory glance.
David Bowie 1947-2016