export module should differentiate against overwrite pre-existing files vs overwrite files we just wrote during import
I see two different forms of overwrite during an export:
1) files that existed, because they were created by something else than the current export (usually this means files that existed before the export started, but if you nitpick you can also imagine files being written to the output directory by another process/user, while the export is ongoing)
2) files that exist because they were written by the currently running export
I enabled overwrite mode for an export, because I did a previous export of a set of files, but now I wanted to export those same files again, but with different quality settings, into the same directory.
However, by coincidence, the set of pictures to export included 2 files with the same filename (IMG_2190.jpg) but from different cameras, and to my surprise only one of them made it into the export. One of them overwrote the other during the export
I would argue that people who enable overwrite mode are doing this for scenario 1. It seems unlikely that anyone would select pictures with the same files for export and want those files to overwrite each other during export. So maybe overwrite mode should only apply for 1, not 2.