[Nition]

What I mean is, they have to read the letters to check whether they're ones they can't read.

[guerrilla]

Fair enough. I think I cracked the case though: they probably have someone who isn't "them" read the letters though, a third party like another law firm or some contractor that offers that service specifically.

[bigDinosaur]

Someone has not read a book even if they read the opening paragraph, so the solution is likely far simpler.