Nielsen DAR API retrieves Cumulative Reach Data for campaigns (similar to Lifetime) and can only retrieve time ranges. This means it will return aggregated data for campaigns still active during the time range specified. For this reason, the API doesn't allow daily breakdown retrieval, or to fetch one specific day (ReportStart date needs to be different than ReportEnd date). It also means that the refetch option doesn't work.
Also, it is not possible to retrieve data from "today" and "yesterday". If today is 12/12/2018, the last data retrievable would be 10/12. Fetching today's or yesterday's data will return an empty extract.
If I fetch 01/12/2018 => Empty rows
If I fetch 01/12/2018 to 12/12/2018 (today) => It will return exhaustive data from 01/12 to 10/12 (last day retrievable) of all the campaigns active in this time range, meaning if a campaign started on 1/11 and end on 30/12, cumulative data from the 1/11 till the 10/12 will be pulled.
- "Campaign dataDate" = Last day of Time Range specified - similar to "ReportEnd".
The data retrieved will be cumulated values from "Report Start" till this date.
- "ReportStart"= first day of the specified Time Range.
If ReportStart is between CampaignStartDate and CampaignEndDate it will contain data.
- CampaignStartDate = First day of the campaign still active during the Time Range specified.
- CampaignEndDate = Last day of the campaign still active during the Time Range specified.
Screenshot of Nielsen Interface: