Heller confirmed the list to be accurate. What he did not confirm was how many on the list were RJ. Of course nobody thought to ask him, because how would more than one RJ make sense? His seemingly personal grudge against Jane makes it seem like an individual. However there are obvious loose ends from season 5 which point to some amount of unity among them. Kirkland and Bertram in the office, Haffner's invitation to Lisbon, Bertram's invite to Lisbon to join in poker etc. 

Those loose ends point to a few options. 

1. There is a group effort to find RJ off the books before Jane does, so that he can be taken into custody and manage an enormous cover up without knowing that they are being controlled by RJ.
2. The group effort to find RJ is to protect him because of how much he knows.
3. The list of 7 each represents one of the 7 letters in the name RED JOHN, and they are all Red John. The name is not of a person but an organization. Martin only knew 1 of them. Red John knew that Jane would track it down to those 7 because those were the only 7 to track it down to. The buck stopped with them. This is why it was so important that Lennon not recognize Kirkland. Red John could kill endlessly until Jane figured it out and still hold to his (their) own rules. For the writer it also means that they can point clues at everybody on the list without diverging from the story line. Pay attention to descriptions of Red John and you will notice they do not all fit.
4. The list is of the next 6 victims. 
5. The list is of the next 6 accomplices
6. Red John Really does have supernatural powers.
7. 3-6