How to check that plan is delegated?
It is not visible from the UI.
The following query can be used to check it from the backend (database):
pba=> select "PlanID","name","Copied_From_PlanID" from "Plan" where "PlanID" = [plan_id];
Copied_From_PlanID contains some ID, then the plan is delegated, this id is the source plan (delegated from).
There is a feature request with id #PBA-58994 ("Ability to find the original service plan of a delegated plan") to implement ability to find out the source plan from BA UI. There is also a feature request #PBA-75891 ("API Call for retrieving root plan of delegated plan") to implement API to get this information.