> I assume that the former publisher of the publication called "Folk Directory" didn't register the name as a trademark?

That would be the EFDSS (I know, cuz I edited the FD for 1977 & 1978). I don't believe it's published anymore so can't see that it would be a problem. There are legal differences between registering a trademark and registering a business name - assuming they did either of those things. More likely they just put it out without bothering, but I don't honestly know. (Somebody correct me if I'm wrong!) In any case, I'm pretty sure that it's a defunct publication so the name would no longer be in trading use.