Hi Travis,
As far as I know, the NSRDB does not yet contain data for 2021. SAM's Advanced NSRDB Download window should automatically show the 2021 data as an option when it is available.
SAM downloads NSRDB weather data from the NSRDB API. You can see from the documentation of the NSRDB PSM v3 API what data is available (see the list of years for the "names" parameter):
developer.nrel.gov/docs/solar/nsrdb/psm3-download/
The NSRDB Data Viewer provides data through 2020:
I'm not sure what the schedule is for updating the NSRDB to include data for 2021. I do see that the NSRDB website lists the year range as 1998-2021, for example here,
nsrdb.nrel.gov/data-sets/us-data. I will follow up if I can find out when the data itself will be updated.
Best regards,
Paul.