Any time you feel tempted to treat collapse as an objective state of a single particle, remember that the collapse interpretation is mathematically indistinguishable from the multiverse interpretation. There's no test for whether collapse has happened other than measuring at both ends and comparing notes… and noticing that nature appears to be cheating somehow.
You can’t tell AT ALL if there was entanglement with one trial. You need to prepare the same state many many times and compare correlations many many times to establish correlations to within some error bound.
