Indeed, this 1000 years is essentially 0 years for dating something with a 50 billion year half life. I would hardly expect them to tell them apart, since 1000 years is such a tiny fraction of 50 billion. However, I might have expected that perhaps 1.3 billion could be distinguished from 0, since it is 2.6% of the half-life...is it your thinking that it should be or that 1.3 billion is still too young?
I’m not in the position to evaluate, but those that are believe that result. The main point is that it is important to match the test to the situation.