How can there be osteoblasts that are not on the surface of bone?

Osteoblasts only may seem not to be on the surface of bone.  Bone spicules are very irregular in shape.  In some places the plane of section can be parallel to, but just underneath their surface. It can then catch a sheet of osteoblasts.  This gives you a chance to look down on these cells as you would a frying pan full of fried eggs.  This is the most informative view of osteoblasts.