When adding events, it's unlikely that most artists will be performing at the same time and one being cancelled doesn't mean others are likely to be, so it makes sense to not pre-fill those two attributes when creating a new relationship based on an existing one that has them.

"Cancelled" requested by agatzk in https://community.metabrainz.org/t/help-test-the-relationship-editor-on-beta-musicbrainz-org/621824/44