In Private workflow, the destinations shown while adding items to an Open Batch are Tentative:
At this stage, we make out best guess as to where Amazon will send the items, but the actual destinations are unknown until the feeds are synced once the batch is submitted to Amazon.
If you are showing more warehouses than normal while listing, these may condense once feeds for the batch are synced (often they do). The destinations are final once you get the Proposed FBA Shipping Page, where you can create FBA shipments for the items.
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?