I have a main bom on the last sheet, and on the previous sheets i show assembly views to the main assembly, I have a bom on each sheet and I want to link the item numbers to the main bom. It seems like it starts a #1 every time i insert a new bom.
see my sample
Im not sure if this is what you are looking for but i have done this before:
For each part create a custom property for item number then when you create the BOM link a colum to the item property.