https://github.com/Kattis/problemtools/blob/92dcbf3fab45ed4c13438511df98ec82fec512f9/problemtools/verifyproblem.py#L212C16-L212C16
Should the above not be a warning, rather than an error? I don't see why it would be an error.
Using symlinks is a nice way of reusing the input/answer files.
For example, you can use the same test cases in two different groups. In one of them validation is case insensitive and in the other a stricter case sensitive validation is applied.