I caught myself thinking: Well, I didn't know that much about Lorca when I wrote Apocryphal Lorca, but then I wrote the second part of the Lorca tetralogy, that will appear in 2018, and so now I'm starting to know a little about him. It will take the third book to really become an expert... And I haven't put hard work in the archives with the manuscripts so I'll never be that either.
That's how it feels from the inside. But from the perspective of any objective person, I am "Professor [of] Lorca" and have been for a long time. Of course I'm continuing to learn more, but the way I learn is to write books about things I'm interested in, so how could my expertise not have increased?