"Please provide three examples of what might qualify as meeting this rather nebulous standard, along with authoritative sources to support your examples."
Obviously I can't do that. Please find someone else to try to do your research for you.
I provided and linked what I believe to be a reliable source for the information. That source referenced THEIR source which was the FDA itself. I took the time to do what you could have done if you had a legitimate concern and looked at the FDA statement as it appears in their Guidance document: Under 2. Demonstrating the Potential To Be a Significant Improvement in Safety or Effectiveness on page 24 it says: "Although such evidence can come from clinical trials comparing a marketed product with the investigational drug, a priority review designation can be based on other scientifically valid information. Generally, if there is an available therapy (see section III.B.), sponsors should compare their investigational drug to the available therapy in clinical testing with an attempt to show superiority relating to either safety or effectiveness. Alternatively, sponsors could show the drug’s ability to effectively treat patients who are unable to tolerate, or whose disease failed to respond to, available therapy or show that the drug can be used effectively with other critical agents that cannot be combined with available therapy. Although such showings would usually be based on randomized trials, other types of controls could also be persuasive, for example, historical controls." https://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM358301.pdf
If the FDA had provided examples I would have been happy to hold your hand further and read them to you. They did not. You can reach them in a bunch of different ways as shown here and ask THEM for some examples: https://www.fda.gov/AboutFDA/ContactFDA/default.htm
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