
The greatest attribute of a Product Manager is a strongly developed ability for metacognition. First, to be able to introspect oneself and see how your words, actions, choices are affecting an outcome. Second, to introspect a process and understand why it is or is not working.
… the past month”. Or “z people made at least one purchase in the last 90 days.” But whatever it is, it should be a signal that they are using their product in the way you expected and that they use it enough so that you believe they will come back to use it more and more.