This is my primary concern. Under normal copyright law you can use copyrighted material under certain circumstances related to 'fair use'. Under 'fair use' doctrine it must not be word for word copy unless it is very limited, like a quotation, and then must have proper citation and attribution. So if I was making a dungeon crawl game that was compatible with D&D but not an actual copy there would be no problem stating that it was D&D compatible as long as I provided citation and attribution to WotC acknowledging their copyright, tradename, trademark, etc. Under the OGL 1.0a I can actually use the SRD 3.5 word for word, but I CANNOT provide citation or attribution back to WotC other than through the OGL itself which prohibits me from even mentioning the product identification.
Now I don't make anything that is directly derivative from the SRD 3.5 other than a few components (monsters and stat system which I state are from the SRD 3.5), but I do use Microlite20 and Microlite2020 components that are also not derivative of the SRD 3.5. However, some parts of Microlite are derivative, but I don't use those parts, only the parts that are unique to Microlite. So I need to include the OGL for those limited parts that are derivative from SRD 3.5, but what do I do with the Microlite portions that I am using that are not derivative of the OGL or SRD 3.5? Under standard copyright law all I would have to do is provide a brief description of what I am using and attribution for Microlite. Or does Microlite fall under the OGL because they used the OGL themselves??? A real nightmare.
I think I can rely upon the OGL 1.0a for past efforts since at the time it was clearly an authorized license. But if I want to create something new in the future that uses nothing from the SRD 3.5, but does use some components from Microlite????? Ahhhhhhhh.