Yeah, but thats the thing, if you have 3 names, and get back 1 name you recruited from the narrator, you CANT assume its solely because they were special roles, yes it makes it slighlt more plausible, but also is mere chance. If you give 3 recruitable civilians (jailer and lawyer included) and get one of them back after narrator randomly drew from them, then doesnt suddenly make the other two BG and D. You might think that as a foolish G and act on it, but you would be hurting your own chances with quick and foolish conclusions.
What it could be used for though, is when you basically know the D (and is being protected, usually BG does that, havent noticed it once in this forum though

), and the BG too, atleast have a hunch, and you put them two in the list, you know you cant get them, but what you are doing is ensuring you get the 3rd name. Which is a vocal and influential civilian you WANT on your side and would improve your chances by controlling votes (thats what I did in above scenario, BG and D was somewhat known, wanted this guy).
Or you can do a minor version of it, of the 3 names, 1 is BG, and the other 2 is two good and smart Cs who you think will be useful. Everything to improve your chances as a G. For example recruit the lawyer, have him save the subject, and see the silly Cs think that saved G is C now
If you let narrator pick for you (randomly in general, not amongst 3), then it wouldnt really be your choice or candidates, no real advantage for you as a G. Imagine if you got a foolish mofo who is already suspicious for everyone, and if by getting to know other Gs, can give it away in the thread by backing or following you in an obvious way etc?