Thank you very much! Yes, I feel sure that Watson's early attempts at puzzling out his flatmate would not have escaped Holmes's notice. I like to think his poor misguided list provided many years worth of private amusement between the two of them. They strike me as two people who would collect quite a menagerie of in-jokes during their years living together :)

It's an old bit of headcanon for me that Watson buys books to commemorate their cases. The bit in the canon that inspired the idea was that passage where Holmes quotes the correspondence between Flaubert and George Sand. Sand is so reminiscent of Irene Adler that I liked the thought that Watson bought the volume for him as a memento of the Bohemian affair.