There are no distinct definitions of mild or severe AS, but there are scales that compare how we answer diagnostic questions as compared to people already diagnosed with AS, measure in "percentiles."
If you score in the 50th percentile on those scales, it means that you answered the questions similarly to 50% of people with AS. If you score at the 10th percentile...
The higher you score on the percentile, the higher the severity is considered to be. Someone scoring at the 10th percentile can be considered to have "mild AS."
But I don't know of any psychologist that would call it "mild." They're either going to assign the DX, or not, as "AS." But this doesn't mean it can't be mild. It can, and that can be frustrating I'm sure, for all the reasons the OP cited.
But I don't think that really matters, because even those who I've talked to who score very high as AS, have the same frustrations. So, mild or severe, our problems are pretty similar.
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I'm not likely to be around much longer. As before when I first signed up here years ago, I'm finding that after a long hiatus, and after only a few days back on here, I'm spending way too much time here again already. So I'm requesting my account be locked, banned or whatever. It's just time. Until then, well, I dunno...