Most of the claims about timing and the Wuhan Flu rely upon data from China. If you look at the ‘tail’ of the infection curves everyone is trying to flatten, that ‘tail’ could extend quite a bit into 2019 beyond December.
FWIW, both my wife and I had coronavirus symptoms when we were on a cruise in September. We flew through Seattle to our departure port in Vancouver. Both cities experience large numbers of Chinese tourists. Our symptoms emerged five days after flying into Seattle/Vancouver.
Actually, the actual curve is not really that steep. The original curve had a margin for error depicted both above and below the actual curve that is a heavy line.
It is the top most band that is the most argued about. It is formed by a variable margin of error that diminishes with time. That makes it look steep.
I can’t cite the actual margin of error but at the greatest value, it exceeds 100%. That represents acknowledged ignorance and inability to accurately predict.
The models that are so roundly rejected by various band wagons carrying happily waving unbelievers produced the curve based on extrapolation of available data from China, Italy and Seattle.