We have made a task step in one of our processes that gets completed after several steps or stages. Each step/stage has a status and we keep its value in the pipeline document. Can we monitor these statuses through a KPI? If so, how, as currently the KPI only seems to monitor data which the task step received and not the data we altered before the completion of this task step?

Try this:

1. use the addEvent web service to send in a custom event
2. configure the new event through the Optimize UI
3. create a KPI to track the status