Well, I idiotically didn't keep those. And the error was nothing to do with the script, don't worry - it was a mechanical problem.
And I wouldn't mind it not using the CPU fully if it went just as fast as the first time but it doesn't. And in the first pass it doesn't matter as much either, because it will only add an hour or so but if it's any indication for how fast the 2nd pass will be, that's the real problem.