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No, you just have to declare what is and is not open content. Nothing in the OGL says that ANY of it HAS to be open content, though anything already declared open content can not be made closed by a later product. So therefore, anything that was previously open content in sources referenced in this book remain open content but new rules in this book are 100% closed content ("Product Identity").
That was unintentional and was just pointed out to me today. We will be correcting that. I intended the rules to be completely open for people to use and play with to their heart's content.