What can make OGL material harder or easier to reuse in other products?

Question

I keep reading about OGL material that is written in such a way that makes it harder to use than normal, and other OGL material that is written such that it's easier to reuse in other products. Specific examples I've heard are that the OGL content in Iron Heroes is particularly hard to reuse elsewhere, and that the monsters at Sean K. Reynolds' website are particularly easy to reuse.

As I understand it, one of the straightforward ways a publisher can make their OGL product hard to build on by third parties is declaring too much, or key parts, of the content to be Product Identity, whether intentionally or accidentally. How does that work exactly?

What other things can publishers do or have done that make their OGL products hard to extend by third parties, deliberately or accidentally? What can publishers do or have done to make their OGL products easy to build on by third parties? What pitfalls are there in setting up an OGL product and its license that can make it hard to reuse when your intention is to make it easy for others to extend?

The ideal answer would be a discussion of things to do and things to avoid—and why—when making an OGL product that is intended to be friendly to third-party reuse.

Answer 1

Easier:

• mark it in the product by different font face, different box borders, different colors for headers (if using color)
• make an absolutely open SRD; no closed content except the OGL text and the SRD name.

Harder:

• No SRD
• use of trademarks within sections otherwise indicated as open
• no indicators of open content other than the OGL text itself

Answer 2

Sometimes the formulation is that "the proper names, personality, descriptions and/or motivations of all artifacts, characters races, countries, creatures, geographic locations, gods, deities, historic events, magic items, organizations and/or groups contained in this book, but not their stat blocks or other game mechanic descriptions" are considered product identity. If the book in question contains all of that (city supplement, monster manual, setting book), then it will be virtually impossible to build on the book, because the stat blocks on their own are not very useful. Effectively the OGL has been used but very little useful open content has been provided.

Answer 3

As I understand it, one of the straightforward ways a publisher can make their OGL product hard to build on by third parties is declaring too much, or key parts, of the content to be Product Identity, whether intentionally or accidentally. How does that work exactly?

Some examples make the text of various powers and mechanics available but not their names or point costs (or point mechanics, for that matter); both Mutants and Masterminds and Monte Cook's World of Darkness have been guilty of this. Keeping names of various setting elements closed as a way to protect IP can also make things more difficult.