Hi Lb,
You are correct in that you should be receiving historical data for all enrollees attributed after your _since date if you are using the Group endpoint. More information about how the _since parameter works with our Group and Patient endpoints is available
on our website. BCDA receives updated attribution information each month. Use the
/attribution_status endpoint to check the last time BCDA received an update for your model entity.
Are you receiving recent claims for those new enrollees? Depending on how the timing of your _since request aligned with the updated attribution, it is possible those enrollees were deemed "new" before your _since cutoff.
If the anticipated new enrollees were not present at all at the time this was sent, please let us know if this is still true after your next request.
Thank you,
The BCDA team