Unique Surface Pattern of Paper

Sounds like an interesting discovery and it came about by accident. The scientist was trying to scan microchips with a laser beam and one fell off so that his laser scanner hit the paper below. He was surprised to see that his equipment gave a reading, so he did a bit of testing and found that all sorts of surfaces could be read for unique surface patterns at microscopic scale. He converts the pattern into a set of numbers that can be used as an id for that specific surface. They article says the reading survives damage to the surface, but I don't understand something - wouldn't you have a problem with registration? Wouldn't you have to be sure of scanning exactly the same part of the surface in order to get the same reading?