Keep making Call of Cthulhu (no one can take Glorantha from you) and you'll be fine.
This is the key underlying assumption when you release a real OGL - that you are confident a 3rd party isn't going to steal your thunder. CoC has such a vast volume of material that they could keep going forever just by updating and re-issuing old books. Glorantha is their thing, especially now that Greg is gone and Jeff can go crazy with the pseudo-anthropolgy stuff, but honestly it's never going to be attractive enough for anyone to even attempt to clone - it's just become way to impenetrable for much of the market. Pendragon seems to be the go-to game for Arthurian fantasy, which is much better protection than disallowing anything even vaguely related under their NOGL.
That said, there are contenders - Delta Green is a very good take on the Mythos, and
Osprey is about to release their own Bronze Age game powered by OpenQuest (which I'm sure will be much more accessible than Glorantha). So nuChaosium have some cause not to get complacent, as their main cash-cow lines are mostly public domain, while Glorantha is at its core a historical bronze age setting that could easily be re-skinned with little effort.
In the meantime, Jeff gets it. Not:
And this really displays why I am tempted to give up answering questions on this forum. Do you really plan to publish something using BRP based on Dunsany's "Idle Days on the Yann"? Really? Or is this just an exercise trying to dance around boundaries you don't really have any interest in actually doing anything with at all?
How hard is it for him to grok that an OGL is supposed to be clear on general cases so potential publishers don't have to ask about every little specific detail?