Too many products...not enough space

My second to oldest daughter has an entire desk top that she uses as a vanity full of every possible hair or skin product that you can imagine, you can barely see the top of the desk. That doesn't include all of the shampoos and acne treatment items that are in the upstairs bathroom. Yet, even with the hundreds of products and different types of make up stacked up, she has the uncanny ability to be able to know when something is missing that her younger sister has borrowed...I've never been able to figure out how she knows, and I've been tempted to just move some things around to see what happens...