Well, part of what Durham wanted to demonstrate to himself was that he didn't need to be running the simulation for the TVC version of him to have a subjective

Well, part of what Durham wanted to demonstrate to himself was that he didn't need to be running the simulation for the TVC version of him to have a subjective experience of the simulation, right? And TVC-Durham has Durham's memories as of the last brain scan, so that's also "him" in a sense. So the fact that TVC-Durham knows that the simulation isn't being run on the outside is valuable knowledge as well. It's sort of a balance between flesh-Durham having assurance that the simulation works, and TVC-Durham having assurance that his subjective experience of the TVC universe is going to continue.