No one in the whole movie ever asks anyone, Did you write this letter' Part of the reason is that no one wants to hear that it isn't for them. As soon as they read it, they want it to be theirs.
I had no idea that 'Less Than Zero' was going to be read by anyone outside of Los Angeles, and it's - believe me, as the writer of the book I'm somewhat amused and intrigued by the idea that 25 years later it's still out and people are still reading it.