When using the Drum Editor, I usually set the Drum Visibility Agents to Show Drum Sounds with Events (Operations Manual, page 784). With the Drum Editor open I can click on different MIDI Parts (OM, page 198), and the MIDI events in those Parts will display in the Drum Editor window.
But I just discovered a bug that can cause major confusion. When I click on a different MIDI Part that has drum sounds that were not in the original Part, the list of sounds displayed by the Drum Editor does not change. As a result, drum sounds that are part of the second MIDI Part but were not part of the first one are invisible! They become visible if I select Show All Drum Sounds and then select Show Drum Sounds with Events again.
This is a bug. The Drum Editor should display all the sounds that have events when it’s set that way. This means that if I click on a different MIDI Part, the Drum Editor should look at that Part and alter its display to show the sounds in that Part.