Rigging a Multi Layer Grease Pencil Drawing

I’m trying to rig a 2D grease pencil drawing, but it’s a side view. So far, I’ve only been able to add weight paint to the middle layer, but I can’t get any for the outer ones.

Is it possible to have one Armature rig multiple layers of a single Stroke? And if so, how do I do that?

I found that if I select the Stroke before selecting the Armature during the Parenting process, it fixes the problem. So my new question is why does this work?

I’m wrong again. I’m paining in one layer. At least I can now select one bone at a time. I guess that selecting the Armature second puts it above the Stroke and the Stroke simply got in the way of selecting individual bones. So back to the original question:

Is it possible to have one Armature rig multiple layers of a single Stroke? And if so, how do I do that?