The BOM is wrong and everything downstream inherits it

What depends on it

A bill of material says what goes into a product and how much. From that comes the material requirement when an order is confirmed, the standard cost used for quoting, and the purchase plan.

Get it wrong and none of those fail visibly. They produce a shortage discovered mid-run, or a product quoted below what it costs to make, and both look like operational bad luck rather than a data error.

Five ways BOMs go wrong

• Scrap excluded, so the plan is short by exactly the amount that is always lost.
• Units inconsistent between the BOM and the purchase record. Grams against kilograms is the classic, and it is out by a factor of a thousand.
• Consumables omitted because they are individually cheap, which understates cost and causes unplanned stoppages.
• No versioning, so a product change leaves historic orders costed against a formula that no longer applies.
• Maintained in one person's spreadsheet, in a structure only they can read.

The last one is the most dangerous and the least discussed, because it works perfectly until that person leaves.

Check it against an actual run

Before a standard cost is used for quoting, produce one batch and compare what was actually consumed against what the BOM predicted.

Discrepancies at this stage are cheap and informative. Discrepancies discovered after six months of quoting against a wrong standard are neither.