Duplicate document numbers are evil

“Our customer has yet again sent us two orders with the same number. One has 15 lines and the other has 10 lines. How should we know which one is correct? They even have the same dates,” is sales assistant Maria worried. “I know, it will be difficult to distinguish between them even by calling and asking client to explain,” agrees her colleague Kaspar.

Prohibiting duplicate document numbers is one of the pillars of well-built information systems. Reuse of document numbers can cause not just confusion and waste of time, but serious errors in fulfilling orders and delivering wrong quantities of goods.

In most software applications, document number is considered a primary attribute (identifier), so it has to be unique and must not be duplicated. There are also programs where the document number might be a secondary attribute, and then some additional fields are used for distinction, such as a sequence number or similar.

However, even if your software allows duplicate numbers, this can cause issues to both you and your partners:

• Accounting – Both GAAP and IFRS agree that document numbers should be unique. This also makes auditing easier. Seeing a lot of duplicate documents may prompt auditors to look for other accounting irregularities, and spend considerably longer time in the process.
• Sales – sending several documents with the same number leads to creating duplicates. The receiving party has no basis to know which copy is correct. This uncertainty often results in calling or e-mailing the sender and asking for a solution. All this means delays in the supply chain processes and final sale of the product. In the worst case, it could lead to out-of-stock situations; making all – the supplier, the retailer and consumers – unhappy.
• Reclamations – in case of conflicts, there is no way to prove which document was “the original/correct” one. It is also impossible for the service provider to help the conflicting parties, as the document log shows multiple copies of the same document.

When the first document you sent to your trade partner was erroneous, never send a new one with the same number. Best practice is always to create a document with a new number and clearly indicate that the previous one was incorrect. In case of invoices, this is done legitimately using credit invoices.

The good news is, most ERPs have a simple functionality of creating both credit invoices and new invoices as a copy from the old invoice. Following the best practice offers you a much quicker and better process to handle problems, might any arise.