See if this helps:
Beginning of Year (BOY) Inventory: What *YOU* paid for any inventory in your physical possession on Jan 1 of the tax year. It flat out does not matter in what tax year you paid for that inventory either. Could have been 50 years ago for that matter.
End of Year (EOY) Inventory: What *YOU* paid for any inventory in your physical possession on Dec 31 of the tax year. Again, it flat out does not matter in what yax year you paid for that inventory either. Could have been 50 years ago for that matter.
Cost of Goods Sold (COGS): What *YOU* paid for any inventory that you *actually* *sold* during the tax year. It flat out does not matter in what tax year you paid for that inventory either.
Take note that it *does* *not* *matter* in what tax year you paid for inventory. But you can not deduct what you paid for that inventory until the tax year you *actually* *sell* that inventory. So if you paid $50 for 5 widgets back in 1960 and you sold those 5 widgets in 2018, you can't deduct that $50 until 2018 when you actually sold those widgets.
