Bill of Material ( BoM ) audit is system specific since it exists along with Materials classifcation + Engg + Costing etc. Hence to audit a BoM, it is esential to know the system.
Presuming that you are referring to SAP,
typically a BoM should be verified for
a) integrity of data. Check Unit Of Mesurement UOM
b) Design of Parent - Child structure of items.
c) Material + Process routings
d) Linking of BoM to other modules ie. how strong /critically inter-linked it is . eg. whether Costing is done independently or derived automatic thru BOM etc
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