If you fetch specific timeseries data from snotel it is possible to get data that is outside the datetime range
i.e. in the url below you can see it ends at 2020-01-01
https://wcc.sc.egov.usda.gov/awdbRestApi/services/v1/data?beginDate=2010-01-01%2000:00:00&endDate=2020-01-01%2000:00:00&elements=PRCP,PRCPMTD,PRCPSA,PREC,SNRR,SNWD,SRADV,TAVG,TMAX,TMIN,TOBS,WTEQ&stationTriplets=1175:AK:SNTL
However you can see in the image below that this url returns data from 2020-09-01 for some reason, which is outside of the range

If you fetch specific timeseries data from snotel it is possible to get data that is outside the datetime range
i.e. in the url below you can see it ends at 2020-01-01
https://wcc.sc.egov.usda.gov/awdbRestApi/services/v1/data?beginDate=2010-01-01%2000:00:00&endDate=2020-01-01%2000:00:00&elements=PRCP,PRCPMTD,PRCPSA,PREC,SNRR,SNWD,SRADV,TAVG,TMAX,TMIN,TOBS,WTEQ&stationTriplets=1175:AK:SNTL
However you can see in the image below that this url returns data from 2020-09-01 for some reason, which is outside of the range