Percussion legends only appear when you are using the five-line staff kit presentation, because when you use e.g. individual instruments or a grid, typically every instrument is already directly labeled in the left margin.
Can I propose the ability to use the Percussion Legend with the grid as well as with the 5 lines stave? This would permit the use of let say a 3 lines stave for peculiar percussion set within the array of instruments one player has.