I'm going to have to take a while to think about this--I'm not sure whether you mean the concept of circular time in the same way that the universe is curved (i.e., there is no percievable end or beginning, things just happen in a cycle), or whether the universe begins again after it ends. The first way, you'd eventually either have to recycle souls or have a universe empty of souls...the second way, the universe might actually come to an end as a result of each soul (assuming there are a finite number in each discrete universe) attaining complete enlightenment, as everything would simply become one; the veil of Maya would be permanently stripped away.
either that every single soul-incarnation is different, like every print of a painting or every $5 note, or that all souls are the same.
That's the most logical answer I could think of. Introducing a conscious divine element into it would add another variable, though, and I'm never sure whether to assume an ineffable God as a presence when I'm talking about the idea of a soul or not. The one's existence would seem to depend on the other's, no?

Do try to find a Szymborska collection! Not all of her poems are online, and they're very much worth a read if you liked Experiment.