They reviewed chest scans from November 1st, and came up with a first case on November 16th.

It begs a question - was the methodology good? Perhaps their method of review was flawed? False positives would explain the low consistent number of cases they found since November.

I think for this kinds of studies they should also do a blind analysis of a pre-covid month or two. Perhaps it would turn out Covid would be found in this data as well.