Based on my (limited) understanding, when one says "monthly growth rate", it means the delta between months. Hence, it is NOT the cumulative version. It should

Based on my (limited) understanding, when one says "monthly growth rate", it means the delta between months. Hence, it is NOT the cumulative version. It should be easy to see why--if you take the cumulative version, then by definition growth delta will always be 0 or positive. Even if you shut down your app next month, growth would be "0", which doesn't make sense, since your app is closed and you turned away 100% of your users so the delta in that (extreme) case would be -100% and not "0". "0" growth means there was no change in users between month.