Understanding schedule snapshots in Flight Info Direct is essential for getting the most value out of your data.
The FILE_DATE parameter in the schedules data is what is often referred to as a snapshot of the schedules database. In the Flight Info Direct record layouts this field comes with the description "Represents the date on which that row of data was uploaded into the database".
Please note that we use schedule snapshots, or FILE_DATE, to configure the frequency of data updates in your subscription. If you have a weekly subscription, you will have access to 1 new FILE_DATE value every week.
What this means is that each FILE_DATE value is, in essence, a complete dataset of OAG's forward-looking schedules data as of that date. Flight records with a FILE_DATE of 2021-01-01 were updated as of 2021-01-01. Although exemptions apply, keep in mind that schedules data is predominantly forward-looking; you should not use today's FILE_DATE to query for yesterday's flight schedules as it would be invalid for the most part.
Keep in mind that each FILE_DATE is a complete record of the flight schedules. If we pretend that on 2021-01-01, Carrier ABC planned a daily, 365 days a year flight till the end of 2021. All 365 days would be included in the 2021-01-01 FILE_DATE. On 2021-01-02 (another FILE_DATE), Carrier ABC did not make any changes, so all the 365 flights are likely still in the record, with the exception of the departure date 2021-01-01 which is now in the past and not valid anymore.