When creating a new part that is similar to another part I will sometimes do a “saveas” of the original part. Apparently Inventor doesn’t update the “Part Number” section in the iproperties with the new File Name. This is a problem when using the Bill of Materials in a detailed drawing because Inventor uses the “Part Number” in the “Description” column of the BOM, not the File Name. It also groups parts based on their “Description” and not their File Name. That means that 2 parts that are physically different and their File Names are different are counted as multiples of the same Part in the BOM.