Incremental Refresh Metrics - How do we know Incremental Refresh is working properly?

With the advent of Incremental Refresh and the ability to share many days' worth of data with consumers of information, the ability to confirm whether incremental refresh is working properly or not is warranted. Please create a set of metrics that would positively confirm that Incremental Refresh is 100% working as intended and designed, and the node isn't just rerunning the entire data pull of all intended records for the time period every time the refresh runs. This could include how many records have been returned in the last refreshes for trending(to show the reduction in # of records pulled since the initial TOTAL record return at the beginning of the Incremental Refresh cycle), duration of the queries in the last refreshes for trending (to show the reduction in time of each refresh since the beginning of the Refresh cycle), and any other metrics that could be pertinent to Incremental Refresh to show it is working properly and as designed.