For me, genre isn't a cataloguing system, or a label attached by the author. It's a pair of spectacles put on by the reader that filters their expectations. There are no rules, only norms, & they only matter in as much as they help the reader 'complete' the text.
My work, ever since I became a professional, has always existed on the hinterlands of categories. As a stand-up poet I sometimes felt outside of every community - not funny enough/too pretentious to be comedy, too lowbrow to be poetry. & then page v stage!
People would get very cross being described as 'performance poets'. Like it was demeaning. I read people saying a poem had to work equally well performed or written down. Which is... well, if you can't add to a piece through your performance, maybe don't charge people to listen?
In fiction, I write stuff that *I* feel is Fantasy but gets shelved in General Fiction. Sometimes I worry it's too weird for litfic, too chin-strokey for Fantasy. Of course I'd love to feel like I had a community I was squarely in the centre of. But I don't think that's genre!
Or at least, I think these neuroses aren't a very fruitful way of thinking about it. Genre, for me, describes a loose suite of schema readers choose from to predict & fill semantic lacunae in the text. Yes I just wrote lacunae. Deal with it.
'Is this story Fantasy?' isn't a very interesting question, to me. A better one might be 'what kind of experience does reading this story as Fantasy produce?'
I'd go so far to suggest that lots of readers bring loads of genre-like lenses to texts without realising. Heteronormativity, for example. They assume every character is straight, & will actually attempt unconscious 'repairs' to rationalise away small suggestions otherwise.
The resting, default state for them is straightness. See cisnormativity, white gaze, etc. Realist/materialist lenses aren't as harmful because IRL no one's oppressed if your crumpets pop up & you wonder if secretly the toast dragon did it.
Genre isn't a club that your work either meets the entry criteria for or doesn't. It's a way of seeing. & each way of seeing yields satisfying results for some works more than others.
THE HONOURS & THE ICE HOUSE both play with genre in a way that some readers enjoyed & others experienced as frustrating, a broken promise, or even an error or a failure of craft. Which is the risk you take when you set up expectations you don't fulfil, of fulfil obliquely.
Traditional Gothic narratives tend not to pivot to armed sieges. Locked room murder mysteries assume the 'detective' will solve the crime. A reader looks for cues for what genre specs to put on, & those cues come with implicit promises of payoffs.
Readers who really didn't enjoy my stuff because they didn't get the payoffs they felt they'd been promised aren't wrong. That's a risk I took & a necessary evil of surprising people - some people don't like surprises, some people just don't like *your* surprise.
At some point in both novels, the genre glasses you've put on for parsing the text stop working. & you've kind of got to switch or grind new lenses. Which is what I wanted to write but I totally understand why some readers find that a slight ballache.
My point is, I don't think applying value judgements like 'authentic/inauthentic' to genres is a worthwhile use of anyone's time. Policing boundaries is about author insecurities. A better question is 'does reading this as [Genre X] help me interpret the text?'