Our database receives data from over 20 different data sources. These data sources feed into our system with varying lag times ranging from 15 minutes (MADIS station data) to 30 days (Reanalysis data). This can result in historical data being corrected with higher quality observations as the lagging (higher quality) datasets feed in.
You may use the "revision_status" field to determine whether or not you will need to retrieve updated data at a later date. The field will return "interim" for data still awaiting updates, and "final" for data that has been finalized. Most historical endpoints reach their final state within 10 days.
As a general practice we recommend querying again for past data to obtain these revisions using the "revision_status" field to determine whether or not to replace data in any locally hosted database.