In Private workflow, the destinations shown while working in an open batch in List are TENTATIVE.
The destinations are not confirmed in Private workflow until the feeds are sent once the batch is submitted.
If you are showing more warehouses than normal while listing these may condense when feeds are sent (often they do). The destinations are final once you get the Proposed FBA Shipping Page, where you can Create the shipments.
If you want to be able to pack while listing, we suggest using Live workflow.
The differences between each workflow can be found in this article: Which workflow should I choose?