I am also not a lawyer, however, under section 15 which lists the chain of content the only thing listed is the Year Zero Engine, i.e. the "SRD." Do not make any assumptions as section 1(e) clearly states what IS product identity. OGL v. 1.0A has been around for a very long time. If you are looking for some further insight into what this stuff all means you should watch the video series by Matt Finch on YouTube. This is in essence where the phrase "Compatible/suitable for use with the world's most popular roleplaying game" came from. Nothing directly used in any of the CRBs should be assumed to be OGL content "as written", there is a comment further up the thread from Free League concerning a question along that line. It is easy to make mistakes and make content fall under the OGL that you did not intend to. For example; if you commissioned a piece of artwork and did not include it as part of your "Product Identity" section you may be violating the agreement you made with that artist. Chances are they are not selling you the rights to the item outright, but just the right to use it in your work, therefore they are not allowing you to then make it Open Content. There is a huge difference in buying art for usage and buying the rights to a piece of art; one you license the use of, the other you are buying ownership.Relevant - the Year Zero Engine, released under the OGL, declares the entire document to be open gaming content. The names of Fria Ligan games (e.g. "Forbidden Lands") are not declared to be product identity, nor are they registered trademarks. So as far as I can tell, the restrictions in section 7 of the OGL don't apply. It seems to be entirely consistent with the YZE OGL to declare an OGL-based product, "Compatible with Fria Ligan's Mutant Year Zero" or similar statements. Is this intentional?
This is a key part of using the OGL in any way; understanding what is/is not your product identity, what is the product identity of FLG and what is OGL content.
Matt Finch's YouTube series can be found starting here: