We were able to unpot our ZZ plant to separate some offshoots. As it turns out, it has a huge root ball, and more removal of the soil reveals the potato-like rhizomes. At first we thought we may have to chop off the rhizomes to separate the plants, but as it turns out, just a slight tug and pull, you can separate them easily. Just be careful in disentangling the roots.
Lower left photo shows one of the plants we separated and lower right photo shows close-up of its potato-like rhizomes and roots.
