Earlier quoted context omitted.
> Depends on what kinds of mistakes the almost-correct approach makes. If it just puts elements in the wrong order, your suggestion works. But if it makes mistakes like duplicating elements, or dropping them, or completely making up new entries, no post-processing will help. The algorithm modifies the original list only by swapping entries. As such, it's guaranteed to result in a permutation.
Yes, in that case the post-processing would work. But it also limits their system to in-place algorithms only.
Why is this limitation? Do you think the algorithm can be improved if it was doing a copy to a new location?