I hope this is the right place to post this... I just had a question about how Pathfinder Infinite interacts with the OGL. I did search the forums to see if someone else had already asked this question, but if they did, I didn't find it.
Anyway, I understand that any Pathfinder Infinite game products have to include the OGL, because Pathfinder itself relies on the OGL. I understand that Pathfinder Infinite allows you to use Paizo IP that wouldn't be available under the Community Use Policy.
What I'm not 100% sure of is whether a Pathfinder Infinite product can include third-party Open Game Content that was released under the OGL but not as part of Pathfinder Infinite. Suppose someone published a book under the OGL in the first-edition Pathfinder days that included a monster I wanted to convert to second edition and use in a Pathfinder Infinite product I was writing. Could I go ahead and use it, as long as I included the appropriate copyright statement in Section 15? After reading over the Pathfinder Infinite content guidelines, I think this should be okay, but it doesn't seem to be explicitly addressed, so I just wanted to make sure...
Obviously not an official answer, but...
As I understand it, Open Content is fair game to use in your Pathfinder Infinite products, in much the same way it is for any Third-Party Publisher to use Open Content. Your only obligation is to include the appropriate Section 15 entry in your OGL.
Common courtesy suggests that it would be polite to ask permission if you're planning to reprint (even if you're doing a rules system update), but this is not obligatory, though it may be noted by the publisher in question and might be questioned by customers, and could damage your reputation.
Having said all that, the OGL is a license and is a legal document. If you are unsure of the appropriate use of it or any portion of it for products you are publishing or planning to publish, it is in your interest to engage a lawyer.