It has been my understanding that the ISS doesn't "refuel", rather the attached crew transport vehicle (the shuttle and now only the Soyuz) used their thrusters to boost its orbit. Searching for information on this I found this Quora answer (https://www.quora.com/How-does-and-how-often-does-the-ISS-ha...) which suggested there had been one test refueling.

I think you saw the same ULA presentation I did, they seemed to think it was very difficult and didn't mention the ISS at all as I recall.