Disappearing Vertex Groups

Sorry, I think I asked this before, but I forget the solution and can’t find the thread.

Anyway, I have a mesh and an armature. All the bones in the armature are named. I parented the mesh to the armature, using “name groups”. Then, under edit mode with the mesh, only about half the bones appear as vertex groups. So I cleared the parenting, deleted all the vertex groups from the mesh, and re-parented it, but with the same effect.

This is the third or fourth object I parent to the armature; would that be part of the problem?