Then again this NY Times article (https://www.nytimes.com/2020/01/01/us/drones-FAA-colorado-ne...) said "local officials were studying the flight path of the drones and coordinating across county lines to figure out where they were coming from."
If they're crossing county lines, that seems like a long distance.
The pattern sounds predictable based on the reporting. Could a sheriff helicopter track them to where they land? Could a photographer team up with a searchlight operator to get a clear close-up photo of a drone, maybe identify the drone make/model, then start to identify the types of equipment (e.g. photo, lidar, other sensors) for clues?
The other puzzling part of this is that if a well-funded entity wanted to test in secret, they could probably find unpopulated areas to test over. Unless the testing relates to features of a populated area.