Types in Common Lisp are really just sets of values. Any value can be of an infinite number of types.
For example, the number 1 is of the type bit (which is an alias for (integer 0 1)). It is also of type (integer 0 2), or (integer -47 234). It is even of the type (or string null (integer 0 277)). So, when you ask (type-of 1), what should be the answer?
Lisp implementations know about some types that are built in. They will usually return the most restricted of those types that they know contains the value. If your Lisp implementation had special handling of numbers in base 5, it might return (integer 0 5) (or an alias of that) for 2.
So that's why the CLHS says that it returns a type specifier, not the type. It also specifies that it has to return something sensible (take a look there).
Your declamation is about the constant named +c0+, but the type-of call doesn't see that constant, it sees only the value coming out of it (think about the evaluation steps). So that declamation cannot have an effect here.
If you want to restrict the type of a value on the fly, you could use the or check-type.