I never even knew that nuclei could be loose and roll around inside pearls until I restrung my BBAs.
I also find those particular akoyas to feel "light." I actually wondered if the nuclei were hollow plastic beads because even when I found a hole, it seemed like there wasn't a tunnel through the bead but a big open space, which made it hard to find the hole on the other side, even with a firm needle. On the plus side, they're not heavy to wear. On the minus side, they're almost too light feeling. But since the nuclei are loose I can tell they have VERY thick nacre, so that's good.