Transplanting on top of previuos grafts

If someone has a hair transplant procedure and 6-8 months later they have an additional transplant procedure, since it can take up to a year for all of the transplanted hairs to surface, what if in the 2nd procedure they place a graft in the same spot as a graft that has not grown yet from the 1st procedure?

Actually, by 8 months, 99% of the grafts that are growing have broken through the skin.  Some telogen hairs may break through later on, but this is not a significant amount.