Yeah it is finding some. But I can't find any type of pattern for why it is finding some references and not others.
For example, I searched an author name in Alfred and it did not find the reference. I searched it in spotlight and it did find the reference. When I search for the same reference by title, I still can't find it in Alfred, but can find it in spotlight.
Another reference I searched for was found by title, but not by author.
I tried adding the kMDItemTextContent in the search filter and ticking the "Show files marked as System Files", but it didn't seem to alter the search results.