——Does the flatness/steepness of the curve possibly indicate that the virus might have been in the US in the very early fall is I suspect?——
I don’t know.
There actually three curves. One is the projection, in the middle and above and below are margin of error curves.
Yes, but the curves I’ve seen do not show the early fall months of 2019. Extrapolating from Dec 2019, one would suspect that there were significant infections in the last four months of 2019.