The fact that the underlying number of resources changes dynamically is not related to whether money keeps track of those resources. The quantitative easing is akin to when an OS overcommits memory and starts doling out more memory than actually exists in response to malloc() calls.
This works because people (programs) aren't going to start using the money/memory right away, or even necessarily at all. Yet, it prevents the system from locking up (or crashing). The fact that not that much memory exists doesn't mean that your malloc() call doesn't let you keep track of how much memory you are allocated. You can't just start writing to memory that hasn't been allocated to you, in essence. The memory (and money) put a bounds on what kind of behavior you can do, what kind of resources you can use.