Yes, exactly. It's tempting to try to compute coefficients X weeks in, so we can forecast X+26 weeks in the future. But the coefficients aren't fixed. Coeffici

Yes, exactly. It's tempting to try to compute coefficients X weeks in, so we can forecast X+26 weeks in the future. But the coefficients aren't fixed. Coefficients change drastically due to public policy, individual actions in response to news and social media, culture of local communities, degree of compliance with public policy, travel between regions with different rates of infection, etc. So you're not fitting a curve to the data, you're modeling dynamic human actions which are not nearly as easy to forecast.