[Observium] Billing Module and Bill Date

I had a question on how the Bill Date is implemented. Currently we have it set to 1 as our normal billing cycle is the 1st through last day of the month.

However the process of getting the API data from Observium and getting that data into our Billing system is a manual process. The API data I'm getting is from the 'type=list' format which doesn't appear to accept start and end dates. I'd like to use this API call simply because it has the billing value of 95th already calculated per bill.

My question is if our billing system makes that API call on April 3rd, what data does it get? Does it get the last full month from March 1st through 31st, or is it getting the data from April 1st through April 3rd?