Hello! My question is about article usage in sentences like, (a) "X wrote a book, song, etc. called "XYZ". On one hand, such sentences provide new information, which is the reason for using the indefinite article. On the other hand, objects in such sentences are obviously definite and unique. If I said, (b) "X came to the conclusion that..." , I would use "the" because there were only one conclusion which X came to, though the sentence also provides new information.
Why is it incorrect to use "the" in (a)?