“Un-referenceable entities” is, after all, a reference.
But not to a single entity. Some expressions in ZFC uniquely refference a single real number. Ie x>0∧x×x=2 or ∃z:z×z=z+1∧z>0∧x+z=2. All sorts of functions, roots trig functions ect can be expressed. There are countably many finite strings of symbols. The reals are uncountable, so the set of unreferenceable real numbers must be nonempty. But in general, testing if an arbitrary string really uniquely defines a value is not easy. It is equivalent to knowing if an arbitrary formula is true or false. So we need to work in ZFC+1. Within ZFC+1, there is a model of ZFC, and so you can take the set of all formulae that can be proved to uniquely define a number within the model, and then take the complement of it. (This is another source of subtlety, The reals within the model may not be the whole reals, which complement do you take)
This gets into some really complicated and subtle bits of model theory. Your paradox, like the set of all sets that don’t contain themselves, is formed by the English language confusing concepts that are subtly different in formal maths.
But not to a single entity. Some expressions in ZFC uniquely refference a single real number. Ie x>0∧x×x=2 or ∃z:z×z=z+1∧z>0∧x+z=2. All sorts of functions, roots trig functions ect can be expressed. There are countably many finite strings of symbols. The reals are uncountable, so the set of unreferenceable real numbers must be nonempty. But in general, testing if an arbitrary string really uniquely defines a value is not easy. It is equivalent to knowing if an arbitrary formula is true or false. So we need to work in ZFC+1. Within ZFC+1, there is a model of ZFC, and so you can take the set of all formulae that can be proved to uniquely define a number within the model, and then take the complement of it. (This is another source of subtlety, The reals within the model may not be the whole reals, which complement do you take)
This gets into some really complicated and subtle bits of model theory. Your paradox, like the set of all sets that don’t contain themselves, is formed by the English language confusing concepts that are subtly different in formal maths.