The price list that applies is the one in force on the day of delivery
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The list that applies is the one in force when the goods moved, not the one that arrived most recently. Take the date of supply off the invoice, find the newest price list dated on or before it, and compare line by line on the item code.
Price Double Check works that way round: a buyer forwards an invoice and the lists by email, and every line is compared against whichever list the delivery date points at. Getting that order of operations wrong is the quiet failure of every hand-built spreadsheet check I have worked with, and what follows is how to do it by hand, including the places where the answer stops being obvious.
The invoice date is the wrong date
An invoice carries two dates and they are not interchangeable. The date of issue tells you when the document was written and when the payment clock starts. The date of supply tells you when the goods moved, and EU invoicing rules require it to be stated whenever it differs from the date of issue. That second date is the one the price attaches to. Goods that left the warehouse on 27 March and were invoiced on 2 April belong to the March list, whatever landed in the inbox on 1 April.
Where a supplier bills a whole month on one document, each line carries its own delivery note or its own date, and the comparison is per line rather than per invoice. Structured invoices make this less of a hunt: the Peppol billing format carries a delivery date and an invoicing period as fields of their own, so the answer is machine readable when the invoice arrives as data instead of a scan.
The order the work is done in
- Read the date of supply off the invoice, or the delivery note reference that leads to it. Fall back on the date of issue only when nothing else is printed, and note that you did.
- Sort the price lists you hold by the date they were sent to you. The email that carried a list is the evidence of when you were told, and it is worth more than the file's own name.
- The list in force is the newest one dated on or before the delivery. If a list prints a valid-from date, that date wins over the date it was sent.
- Pick the column addressed to you. A manufacturer's sheet often carries a recommended retail price, a retailer price and a distributor price, and only one of them is yours.
- Join the invoice to the list on the item code, never on the description. Across one real set, 335 lines out of 442 had a description that did not match its own price list line word for word.
- Compare unit prices, allowing a cent per unit for rounding: lists carry four decimals and invoices carry two, and half-up at the line is what keeps a check from reporting noise.
What each document settles and what it does not
| Document or field | What it settles | What it leaves open |
|---|---|---|
| Date of issue on the invoice | When the document was written, and the payment terms | Which price was agreed |
| Date of supply on the invoice | Which price list was in force for those goods | Which column of that list is yours |
| The email that carried a list | When you were told about a price and what you can hold the supplier to | Whether a newer list existed and was not sent |
| A valid-from date printed on a list | The first day the list applies | Anything about the list it replaces |
| An increase announcement | That something is going to change | Which lines change, and by how much |
| The order sheet | What you expected to pay at the moment you ordered | What the supplier treated as in force |
A list with no valid-from date runs until the next one arrives
Most supplier lists state no validity period at all. In practice they run until replaced, which works until the replacement never comes. In the set behind this service the current year's list was never sent, so the previous year's remained the only basis anyone had, and one line was billed at €13.23 against €11.235 in it — 17.75% on the unit and €47.76 on a single invoice. Nobody noticed for a year.
The remedy is a sentence in an email rather than a system: ask the supplier for the list currently in force and the date it took effect, and keep the reply in the same thread as the invoices. A supplier who cannot produce one has just told you that the list you hold is still the agreement. That is a stronger position than it sounds, and it is the position an increase letter is worth reading against.
Two files under one invoice number are one invoice in two versions
The identity of an invoice is the supplier and the number, not the file. The same set held three files under one number, all with the same date and three different totals: €3,472.70, €3,482.25 and €3,480.34. Two more shared another number, and a credit note cancelled only the second of them. Comparing the wrong version against the right list produces a finding that evaporates the moment the supplier answers. Say that the versions disagree and ask which one stands, rather than picking.
Sometimes the invoice is ahead of the list
One item was invoiced at €1.26 from March while the list in force said €1.176. The €1.26 appeared in a price list only in October, seven months after the buyer had started paying it. Read one invoice and it is a small difference worth a shrug. Read the months together and it is a price that changed without anyone agreeing to it, and the list that eventually arrived is the supplier's own record of when the change should have started.
This is the case for keeping every list you have ever been sent, in the thread it arrived in. Drift is only visible across documents, and the cheapest archive is the mailbox you already have.
W skrócie
- Which date to use when the invoice prints only one
- Use the date of issue and treat the result as provisional. If the finding is close to a list change, ask for the delivery note before writing to the supplier. A difference that disappears once the real delivery date is known costs more credibility than it was worth.
- What to do when two lists share a date
- Treat them as a version conflict rather than choosing the cheaper one. Two lists with one date is the same problem as two invoices with one number, and the supplier is the only party who can say which stands.
- Whether an announced increase replaces a list
- It does not. An announcement says that something will change; a list says what each line costs. Compare the two when the list arrives, because the lines that move are rarely the lines the letter mentioned.
Forward one invoice and the price list it should have been billed on, and the comparison comes back by email, keyed on the item code and dated against the delivery. What a difference is worth once you have found it is the subject of the arithmetic of margins, and the prices are on the home page.