How can we use Lookback API to get all previous values of Schedule State?
Here is an example Lookback API query you can use:
https://rally1.rallydev.com/analytics/v2.0/service/rally/workspace/<<Workspace Object ID>>/artifact/snapshot/query.js?find={"ObjectID":<<Artifact Object ID>>},_PreviousValues.ScheduleState%22:{%22$exists%22:true}}&fields=["ScheduleState","_SnapshotDate","_SnapshotNumber"]&hydrate=["ScheduleState"]&compress=true
This query is requesting all previous snapshots of the artifact that had value for Schedule State. The value is then hydrated to display the field's string (instead of the numeric value).
Here is a screenshot of the JSON output: