"Diagnosed" versus Self-Identifying

Just about four years ago I was able to see a Neuropsychiatrist and get an "Official" diagnosis as inattentive-type ADHD, but that and my IQ was all I was tested for. In the last couple of months, my therapist and I have determined that it's *highly* likely that I am actually AuDHD, but right now (and for the foreseeable future) there's simply no way I can afford to get an official assessment/diagnosis, no matter how much I would like to get one. I have completed several self-assessments online (doctor recommended ones, not just pop-quizzes out of Cosmo magazine) and yeah, AuDHD really fits my brain so much better than just ADHD.

I've been spending more time with my family (my parents are in their 80s and my sister and I are both in our 50s) recently and when I was visiting my sister, she turned to me and suggested that I really should NOT call myself a person with Autism in any way until I have a formal, medical diagnosis, because 1: I'm not a doctor, and shouldn't be self-diagnosing, and 2: It's some kind of insult to people who actually DO have Autism?

I totally get how irritated lots of us get when neurotypical folks toss out the "Oh, I'm so ADHD - LOL!" when they forget their keys the one time, and how that can be problematic because then it feels like the world sees our struggles as a joke, but who has a few grand in cash that they can just plunk down to get a neuropsych assessment these days, though? (*I* certainly don't!) So now I am worrying about telling anyone anything more than my "official" ADHD diagnosis, but NOT including the Autism part feels like I'm hiding something I should be ashamed of? Or that by not sharing it means that I will be somehow held to a level of expectation that I might not be able to meet? (Does any of this make sense - I'm so sorry if I'm not being very clear)

Are there - if not rules - some kind of general understandings of when it's acceptable to 'self-identify' versus when we really ought to have that piece of paper with the doctor's signature on it?