I thought that having done the Amazon ad for Conventions – and it is attracting interest – “How about the earlier books?”
So you may stumble upon these, too, on Amazon and the Kindle:

In prepping them, I had again noticed one of the genre choices: “New adult and college.” Of course I had an idea what that might be, but I had never dug into it in any detail. So I decided to start at today’s center of all knowledge: Wikipedia:
New adult (NA) fiction, also rendered as new-adult fiction, is a developing genre of fiction with protagonists in the 18–30 age bracket. St. Martin’s Press first coined the term in 2009, when they held a special call for “…fiction similar to YA that can be published and marketed as adult—a sort of an ‘older YA’ or ‘new adult'”. New adult fiction tends to focus on issues such as leaving home, developing sexuality, and negotiating education and career choices.
The genre was originally met with some criticism, as some viewed it as a marketing scheme, while others claimed the readership was not there to publish the material. In contrast, others claimed that the term was necessary; a publicist for HarperCollins described it as “a convenient label because it allows parents and bookstores and interested readers to know what is inside”…
The opinions of “some,” “others,” or still “others” who may have “viewed it as,” “claimed,” or also “claimed…”
Outsiders’ takes aside, do actual authors attempt to fit their fiction into someone else’s narrow shelf definition of a genre label? Some probably do, or try to.
But I suspect most do seek to write to their own vision. I do:

“Miss Carolina Beckington” there is still age seventeen and “Mr. Rutherford” recently turned twenty-two. Does that make her “young adult” or on the cusp of “new adult?” And is he?
Not really in my opinion, and I wrote it. One of my aims is also never to “talk down” to readers. Whether in historical fiction or in “contemporary” fiction, in my view any 18-year-old plus reader of a book that includes “age 18” and up main characters is simply an adult reading about other adults.
Have a good day, wherever you are. 🙂
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UPDATE: I gave in and placed the Atlantic Lives novels under that “new adult and college” Amazon genre for the ads. They are for, simply, adults, I feel. But someone else would probably say, “Yeh, but they are age 24…” Ugh.