When you post a physical inventory transaction, you can do it as a partial inventory or a full inventory. If it is a partial inventory, only the products referenced in the transaction will be adjusted. If it is a full inventory, any products not listed will be assumed they are not in the zone (or have a 0 count). It is very important that you understand the difference. When you post a partial inventory, the system, does the work for you to turn it into a full inventory. If you go back and edit it, it will include all products and not just the ones you partially posted.
Process is as follows: