The naming of each version is incorrect.
P3 is Primavera Project Planner. When launch, a twin is with it, it is Finest Hour. P3 offer planning unit in Day and FH offer planning unit in Hour, which is same as P3e
Since P3 is 16 bit flat file design, P3e (NOT P3E) launch to cater 32bit and more functions when implement on organization. P3e full name is Primaver Project Planner for enterprise.
Since similar project management solution apply to different industry, so P3e is major for construction and engineering field, for IT or project setup or others industries, same solution but in other name for identification.
Then users comfuse for those products, they think it is different but actually all the same, so the whole series rename to P3e/c (Primavera Project Planner for engineering and construction).
When launch P3e/c v5, there is a significant change and they re-brand it to P5, now is P6 and the recent is P6v7