This is another "Sigma Summarizes Information Because It's All So Complicated And In-Depth" posts.
Iceberg Theory was first proposed in the Archive in 1952. It has since become the leading theory concerning the nature of the PREs.
The premise of Iceberg Theory is simple: There is only one of each PRE in all universes. However, the PREs, in their true forms, are so vast and immense that only a small piece can be seen and experienced. A piece protrudes into each universe, just like only the tip of an iceberg protrudes over the water.
For example, taking the phenomenon of Dimensional Bleeding into account, there are conflicting reports regarding PRE05 "Wooden Girl". Some accounts have her appearing as a literal puppet, others have her as a human covered in wooden armor. Some have heard her speak, others claim that she never speaks. Some reports claim that her servants are divided into a rigid structure, other reports claim that she keeps her servants in a chaotic, Darwinian system. Dimensional Bleeding explains these various accounts as occurring in different realities. According to Iceberg Theory, however, despite these accounts taking place in different universes, with PRE05 showing radically different behavior, there is still only one PRE05. The versions of PRE05 observed in each reality are merely parts of the whole.
It's like if you took four small vitamin cups, filled them with water, and placed them all side by side. Then you put your hand down there so that each finger was in a different cup. Your fingers, while similar, are still different. So while a part of you is in each cup, it's not the same part. Well, imagine the cups are universes, and imagine you are PRE05. Your fingers are what the denizens of each universe encounter.
That's right: according to Iceberg Theory, the PREs, no matter how powerful or vast they seem, are merely fingers of a greater being.
There's also an offshoot known as the Multi-Tipped Iceberg Hypothesis, which goes even further: all the PREs are in fact extensions of the same being.