I learned long ago that the thicker these stickers get, the easier it is for a thief to scrape the stack off without damaging the top sticker, and re-gluing the stack to their license plate when they don't want to pay for a new registration sticker for their car. Cops think you are current on your registration if you are displaying the currently proper color sticker so you won't get pulled over with an expired sticker.... I even go one step farther and not only do I keep only one sticker on my plate, but once I have the new sticker stuck well onto my plate, I take a razor blade and put an "X" into the sticker and maybe a few more cuts. This way, if a thief tries to steal the sticker, it deters them once it starts coming apart in pieces or hopefully they see the cuts before they even attempt to remove it...... Just an old habit I have. Plus, it really does look tacky when a car has many years of stickers stacked on top of each other.