I think evaluation of prognosticators needs to take more account of early predictions (as I post about on 538 here). If you only focus on your final forecast, what stops from you posting garbage until shortly before election day?
But races can change dramatically until the election day. So if for example you see a big difference between an early forecast and the final results it doesn't necessarily mean 538 was wrong, just that things have changed. Sure, you have to take that into account. But it's really just another form of uncertainty that exists in other ways right until Election Day (for instance polling errors). Your 20% predictions two years out or two days out should still be right 20% of the time. The big problem for evaluating predictions, early or late, is the small sample size of elections 538 has covered thus far.
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