We built this, and you webhook, or build endpoint, post out the subscriber unique id combined with campaign unique id since it never changes, then in that time period for that campaign only occurs one time ever with that subscriber unique id, and then you know how much sent for that time to those users, then from ONLY those users so that time only to present or cut of date of engagement, you know from those users who opened so how many opens divide by sent then, and for clickers same deal, but it is all about subscriber id's with campaign id and send date range, and cut off date you program, last year if you looked at a week of openers. gonna be pretty good but if you looked 4 days after that period of time last year, to see how it was back then 4 days out from that week of sending to how it is now for the same zone of the year, great, cause something looks good 1 day after sent in a flow, that is amazing!! but if it took 19 days to get to that, not so good, so your end date for opens and clicks on that send period MATTERS! but yah, MZ has all the stuff there to do anything if you can, and will go deep