About Blend Vertices
All sections of a swept blend must have the same number of entities. When one selected section of a swept blend has fewer entities than other selected sections, a blend vertex can be used as a entity. A handle on the selected section allows moving the blend vertex. It automatically snaps to a point or vertex on the selected chain. A blend vertex can sit on a point located on an entity.
When more than one blend vertex can share the same location, an indicator displays the number of vertices at that point.