We want to share that the archivedAt API response value has a new definition for most endpoints. Previously, a bug caused archivedAt to return a timestamp showing when the object was last modified. Recently we began instead to return the timestamp of when the object was actually deleted.
Note that this change is not yet in place for the contacts endpoints. We'll reply on the forum thread and provide a new changeling post when these endpoints have been updated.
Note also that deleting an object has never updated its last modified time, and that continues to be the behavior with this change.
If you have any questions, please let us know in the forum thread.