A: Embarassingly enough, prior to 2017 we had a small bug in our billing system that was not tracking usage for the last day of the month.  As of first days of 2017, this issue has been corrected and monthly bills should be correct.  Do note that we assume that each resource consumes 730 resource-hours per month and track usage on an hourly basis.  Those customers who are monitoring 5 resources (or 25 resources on VLM1 plans, or 100 resources on VLM2 plans) might see a slight uptick in their monthly invoices on months that have 31 days.