How did scientists first measure the size of the universe?
With unit of time as million (M)/billion (B) years, the distance of the farthest star-cluster is estimated. If this is N M/B light years (ly), the size of observable universe is at least N M/B ly.
As of now the distance of the oldest star cluster is < 13.82 Bly, by some millions of ly.
If we detect light that had come from a star cluster N B years ago, the distance of the source that existed N B years ago was N Bly.
To know whether the cluster exists now, it would be a wait for N B years more, for that light to reach the Earth.