Difference between face count and vertex count?(Voxel draw optimization)

[anonymous_user_369165731 (anonymous_user_36916573)]

The blender api says:

Vertices can only be shared between faces if:

1. They are at the same position
2. UV coordinates are the same
3. Their normals are the same (both polygons are “Set Smooth”)
4. They are the same color, for example: a cube has 24 vertices: 6 faces with 4 vertices per face.

The vertices will be sharing position, normal and uv. (and probably color)
So welding should be possible.

This article says that vertex count is more important:

Polycount vs Vertex count

Problem is I get stellar face count reduction but meager vertex count reduction…

Also using an actual voxel engine would be way above my skills.
Meanwhile this is educational.

I will update the picture to clear up the 10% difference.