The general bill of materials (GBOM) lists all parts, part families,
and products and their subtypes of a feature or product.The Precise
BOM is generated based on the GBOM objects related to those products
and features present in the product configuration after evaluating their
inclusion/exclusion rules.
If a product is added as a feature
or a subfeature, then its GBOM items are shown in the Precise BOM. But
if the product is added as a GBOM item, then only the product is shown
in the Precise BOM and not its GBOM items.