It's not clear the best way to handle this and how high of a priority this is, but the issue is as follows. The IL state water survey data has all previous years data in a single file, CMIday.txt and for the current year (2020) in CMIday20.txt. When the calendar year rolls over to the next year (2021), it expects CMIday.txt should have all the data through 2020 and a new file, CMIday21.txt for the current year. If not, it fails because there is no file called CMIday21.txt. 

From Slack: 

There are two issues, 1) was that it expected in the current year there should be a file (e.g. CMIday21.txt for 2021), and 2) it assumed once the year changed, all data was available for the past year so if the last day you had data for was 11/30/2020, it would start gap filling at 1/1/2021.