This doesn't really change my reading of those statements; the issue to me is that "there is such a thing as X" sounds to me like an existential proposition, i.

This doesn't really change my reading of those statements; the issue to me is that "there is such a thing as X" sounds to me like an existential proposition, i.e. "X exists". The idea that an abstract descriptive concept only sometimes exists doesn't really make sense to me; it sounds like saying that addition only "sometimes" exists because there are equations that only use division and not addition.