I'm trying to build something like an inverted funnel, and I don't know how to do it: we have two events, one is Started Job and another one is Completed Job. Technically, you shouldn't be able to complete a job without starting one, but it's pretty clear that it's happening in our data. To debug/investigate it would super useful to ask "how many people (and who) have completed jobs without first starting them? what percentage of completed job events don't have a precurson started job event?" that sort of thing, but I don't know how to do it with the current tools