Thanks for the responses from Paul Barrington and Matt Smith, but they don't address the question. Having pondered it further, I will say what I think the answer is.
Suppose there was just one NBN data set that contained relevant records. You would obtain the permission of that dataset owner to use their information and I think it would be reasonable to mention in the report that that was the only useful data set without having to get the permission of all the other owners of data sets that contained no relevant records. So if there were no NBN datasets that had records for the area of search, I think you could say as much without having to get anyone's permission.
If anyone in NBN disagrees, I would be grateful if they could say so and explain what the correct procedure would be.