Purchase orders and inventory are usually treated as separate concerns and they meet at exactly one moment: the goods receipt. That single act increases stock on one side and enables the three-way match on the other. Software that treats them as two entries asks the same person to do the same thing twice, and the second one is the one that gets skipped.
One act, two consequences
Receiving a delivery against a purchase order line raises the stock figure and records that the order has been partly or fully satisfied. Where systems separate them, whoever takes the delivery records it once, usually into whichever system their manager cares about, and payables discovers the gap when the invoice cannot be matched.
Why stock accuracy and match rate travel together
Both depend on the same discipline. An organisation with reliable stock figures nearly always has reliable receipts, and one whose stock counts drift is usually failing the match for the same reason. That connection is a useful argument when the receipt step has no owner, because it gives two departments a shared interest in it.
Where to keep them separate
Valuation, cost methods and write-downs belong to stock accounting and to your accountant. Payables needs the quantity and the date, not the valuation. Keeping that boundary clear prevents a payables project acquiring an inventory accounting scope it cannot deliver and was never asked for.
Questions people ask about purchase order and inventory management software
Do we need inventory software for three-way matching?
No. You need the receipt recorded against the order line. Full inventory management includes that and much more.
What about non-stock purchases?
They still need a receipt in the sense of somebody confirming delivery; it just does not move a stock figure.
Which system should own the receipt?
Whichever the person taking the delivery will actually use, because ownership has to follow usability here.