Report COGS for the BOM items in an Inventory Assembly

It does not work like that

you define the items used to make the assembly item, then you issue a build command
when the assembly item is built, the average costs of the items that make the assemble are added and that total becomes the assembly item average cost.  Inventory items used in a build and no longer exist, they are part of the assembly item

Assembly and inventory items are held as assets in QB.

When you sell the assembly item, the average cost of the assembly item is removed from inventory asset and posted to the expense account (COGS) on the assembly item screen.

there is no real reason to have more than one COGS account IMO.

@Rustler, thanks for the quick reply.

I am being asked to show how much we spent on BOM components for the assemblies that have been sold this year.

Instead of presenting a single value that summarizes cost of all the BOM components, I need to show that we spend a total of $X on Component A, $X on Component B, etc.

Is this not possible?

That would be hard to do even manually

QB keeps average cost, so as you buy replacement inventory, each item average cost may go up or down.  That average cost on the day the assembly is built is what is used for each build, and finding that average cost historically is almost impossible.

However if item X is ONLY used in an assembly, then a purchase report on that item could be used, and extract the qty used in the date rage, do the math for total cost item X

The problem with your request is that the BOM components never flow data to COGS unless you sell them Individually. From the perspective of the assembly, the cost as asset value still is invested in asset value from the Build. There is no COGS event, in other words.

You don't even have sales by Item reporting or profitability for individual components that are only used in the Build. Literally, the value simply is in a different Item, but still in Asset.

You have better reports than the P&L, to see Costs; you have Item Based reporting.

Run your Inventory reports, such as Valuation reporting, purchase reports, etc.

And your best reference for the chart of accounts is the tax form this entity files. There is One COGS line there. That is all you need in QB, too. The Item based reporting not only gives you breakdowns, but it also allows you to include quantity in your analysis. The P&L is supposed to be Simple to read. It is the performance of the entity. The Operational reports, such as Sales and inventory, are your Analysis reports.