OTOH, that all/winter flu outbreak was widespread enough that research hospitals would have seen the x-rays and CAT scans, and the COVID pattern is distinctive enough that even normal radiologists would have begun picking up on it.
That makes an assumpton that a radiologist was even used or needed. How many people don’t have insurance and don’t even go to the doctor uness they are near death? A LOT!
We’re not talking about 50 people or even a hundred. We’re talking about thousands - tens to hundreds of thousands, perhaps millions, had this flu go through during the time period discussed.
Ok, so the title asks if it has come and gone for "most" of the US. Now, THAT I do not believe there is evidence for. That would be wishful overly positive thinking. But I do believe firmly that it has been here and passed in pockets in relation to late November/to late December travel. (especially as originating in Northwest US to Vancoucer(ish) BC. and NY state) Travel since then is another story.
The pockets likely in rural areas where it is more likely to just fizzle out on its own. Now the bigger cities (some with) with older populations are getting hit and that's where the death toll could climb. But we still don't even have widespread testing.