fitDataWDR returns a list of 3 data series. Each data series is a list of pairs of values of the form {time, number}. The first data series in the number of confirmed cases (not the cumulative number), the second is the number of recovered cases (which happens to be cumulative because it's a sink), and the third series is the number of deaths (also cumulative because it's a sink).
For example the first 5 elements of each series for Beijing is
In[18]:= fitData =
fitDataWDR[Entity["AdministrativeDivision", {"Beijing", "China"}],
"21 Jan 2020", "dateRange" -> All];
In[19]:= Take[#, 5] & /@ fitData
Out[19]= {{{1., 14}, {2., 22}, {3., 35}, {4., 39}, {5., 66}}, {{1.,
0}, {2., 0}, {3., 1}, {4., 2}, {5., 2}}, {{1., 0}, {2., 0}, {3.,
0}, {4., 0}, {5., 0}}}
If you don't have data for one of those series, then leave it out of the list of series, and also leave the corresponding model out of the list of models given to sumSquaredError.
Hope this helps!
