I don't think the Mangione case is a particularly good example, you wouldn't use a 911 call by a random McDonald's manager to disguise parallel construction.

The caller is easy to identify, how could the government ever trust this person to not reveal their parallel construction? If they were planted by the government, that'd be extremely difficult to hide. The government also likely wouldn't be able to compensate them in any meaningful way for telling such a lie.

The Kohlberger case also does not suggest parallel construction, the DOJ policy isn't binding and the DOJ can in fact legally violate that whenever they want.