The thing is, entanglement can actually be break, well, largely, when one wave is isolated and has nobody to interact with, they are temporally disconnected from the rest, and thus only itself, and its byproducts as it decays, are entangled. You can achieve this through reaching 0 kelvin in the experiment area. We can also make two sole waves interact, and become entangled while disentangled from the rest, and then connect both back to the universal entanglement, and we will see the properties of the two particles we entangled first are still correlated (just like all particles in the universe are from each other), but we can keep it track as we became aware of the fact now.