Maybe both of these are true: we have found only a few instances of voting by illegals, and many illegals have voted but we just haven’t found it yet.
FWIW, Allegheny County was one of the very last counties to give its results in Pennsylvania in 2018, just as we were looking for one more state to put Trump over the top. I think they were in fact far later than Philadelphia, which is usually last. I can’t dismiss the thought that Dems had seen the unthinkable result coming to pass and were trying to reverse engineer the Allegheny County numbers after the official precinct closing time.
They are likely to go all out for the mid terms. I hope the normals are braced for impact.