I think i know what's going on with procedural generation in modern games. The key to preventing duplicates comes down to using specific mathematical seeds that feed into complex algorithms, really clever stuff when you think about it. The system takes a base number, in one case it was literally just a dev's phone number, and uses that to create consistent outputs every time you visit the same coordinates.

What makes this work is the way it handles creature generation through some pretty sophisticated math. When generating a new creature, the system uses something called the superformula along with l-systems to create variations that actually make biological sense. The cool thing is, it doesn't need to check if something's been made before, because the math guarantees everything will be unique based on the coordinates and seed values.

The really interesting part is how it maintains consistency without needing massive databases. Since the same input values will always create the same output, you can revisit locations and find the exact same creatures, but move to a different spot and the math ensures you'll see something completely new. With quintillions of possible combinations, the chances of seeing the same exact creature twice in different locations is basically zero, unless you're returning to the same spot.