Regular evidence will suffice. If people can make the material and levitate a small permanent magnet above the sample at room temperature, that will be sufficient.
That's a pretty high bar. Everyone has their own threshold of skepticism, but if NREL announced next week that they followed the recipe and it was superconducting at room temperature, I'd be willing to bet money on it being real.
I think that "reproduced at 100 labs" is near the level of reproduction at any university lab, maybe even as a part of students coursework. Which would actually be great, since we don't have trouble reproducing some other important electromagnetic and quantum phenomena, like light diffraction, at an ordinary university lab.
