As you may have noticed "item" has two meanings in Fusion 360 Manage.
The first meaning is technical: everything is an item in a workspace. A document in document workspace is an item, and a supplier in a supplier workspace is an item. Each item in this context has an internal id that we call the DMSID. And you can use this internal number to pinpoint a specific revision in a revision managed workspace (each revision has a different DMSID). You could draw a conclusion here that Item Numbers are distinct for every revision, but I wouldn't.
The second meaning is the representation of records in the "Items and BOM" workspace. The "Items and BOMs" workspace holds items that are commonly referred to as parts; so in this case, the Item Number and the Part Number are the same thing.
Your customer/company may redefine these terms and may require both Part and Item numbers. That's totally acceptable. For example, some customers will reidentify Vendor Parts such that there is an Internal Part Number and a Vendor Part Number. But apart from that, I haven't seen companies maintain both Item and Part Numbers. Every number you maintain is going to cost you something.
