Method

Three files, not forty

A batch that went wrong usually went wrong the same way in every file, which is what makes spot checking work.

Catches a wrong setting — the whole run inherited it.

Catches anything that drifted or was cut off as the task got long.

You know which file it is: the one with the odd layout, the extra pages, the different source. If that one is right, the ordinary ones are.

Three files, under a minute. Opening all forty takes longer than the batch did and finds the same problems.