Windchill allows the use of gathering parts. These parts can be suppressed in BOM reports while underlying parts are rolled up to a higher level with the correct quantities calculated.
However, if ESI is used to send the BOM to a distribution target, there is no possibility to suppress the gathering parts. Customization is needed to create the same functionality as offered by the standard BOM reports.
We request the gathering parts functionality in the ESI BOM release.