BUR #6391 has been approved by @evazion.
remove implication stitched -> third-party_edit
stitched images are more often than not the joining of scans or digital doujinshi that were originally thought as a single image but had to be split for publishing reasons. I don't think rejoining this kind of content can be counted as a third-party edit, because there's no actual change to the picture itself.
Same reason why fixed should not imply third-party edit.
We have a lot of these under stitched scan for example.
Updated