Also, the difficulty of identifying someone probably looks like a power-law curve, meaning that most of the "total difficulty" is concentrated in a small group, the ~13% that can't be identified.
In other words, even if one person is extraordinarily tricky to find [0], their share of the total un-findable-ness does not diffuse outwards to help anybody else.
[0] http://tailsteak.com/archive.php?num=433
