I've read many articles and posts where physicians and clinics write that follicular unit transplantation technology in combination with custom made incision instruments provide a totally natural hairline. While these technologies and technique are the state-of-the-art we cannot assume these tools and building blocks will provide undetectable results in the hands of all physicians. At you state, nthmainneighbor, the truth is that most clinics will not provide the type of undetectable hairline that is seen in the photos above. If you have bricks and mortar is does necessarily mean you have the skill to build a house.
Follicular units are the building blocks here, but the natural hair line is the result of surgical skill.
Doing more that one producer is not uncommon but it depends on the patient's goals. Many times the first procedure will provide the most dramatic results. For example, if you are totally bald in an area and plant 2000 grafts into it, you will have an infinite improvement. If you plant 2000 more grafts into that area at a later time, you only double the improvement. This guy had alot of loss so he really went 0 to 60 iwith one big session.