Slightly different subject but I am finding that the more additions I get in my passport, the more densely they overstamp all my earlier pages, My travel is constant (i.e. I would say that the amount of stamps and visas I receive are pretty much the same every year) and I was at a rate of a new addition every 7 months for the first two, then every ten months for the next two, every year for the next two. I would estimate (becasue I am not going to count every page) that currently my pages probably average 9 stamps per page throughout my entire passport, once it gets to a certain thickness, most PP stampers are just too lazy to find empty spaces.