Not sure about the biggest uncovered in history but a district in NC went without representation for almost 2 years because they couldn’t certify an election due to fraud in 2018.
I don’t know that it’s enough to overturn an election but that doesn’t mean we shouldn’t find out, just because it was never found to be this large scale doesn’t mean it wasn’t this time. That would be like saying we looked at Enron’s books and there was some shady accounting but that happens in all companies, let’s not try to get to the bottom of it.