Provide both the document and its context

Send the invoice and tell your accountant when it arrived. They can see the issue date on the document; your message explains why it was missing from the original submission. Let them determine the accounting or tax period.

In the example, an invoice issued at the end of August arrives on 8 September. You sent August's records on 5 September. The accountant needs the new document and to know it was absent from the original package. You need not determine its accounting allocation yourself. Truthfully describe when it arrived and which purchase it concerns.

If a filing deadline or closed period is involved, contact your accountant directly. A universal rule such as “late invoices always belong to the next month” could incorrectly simplify your circumstances.

A new invoice, another copy or a correction?

Before forwarding, compare it with what was already handed over. Some suppliers send the same invoice repeatedly. Sometimes a corrected buyer or changed document arrives with a similar name. A recurring subscription may have the same supplier and amount but be a new document for the next period.

The filename alone is insufficient. Check invoice number, buyer, date and content. Preserve the connection between a correction, original file and supplier message. The accountant then receives information about a change rather than two nearly identical unexplained attachments.

If unsure, describe that uncertainty. “The supplier sent a new PDF with the same number but changed the buyer” is more useful than your own definitive “duplicate” label, which could cause an important document to disappear.

Send a clear supplement

Usually the easiest approach is to continue the original handover and mark the message as a supplement. Send only the new part unless agreed otherwise. Resending the whole package forces the accountant to identify the added file.

If you have several businesses, name the one the addition belongs to. If you send it in parts, label them “1 of 2” and “2 of 2,” for example, so your accountant knows whether all messages arrived.

Select the text, copy it into an email and fill in the details in square brackets.

Do not silently replace what someone is already using

Replacing a file in a shared folder is easy, but the accountant may already have downloaded an older copy. Announce document changes and keep a traceable relationship between versions. The folder's current contents are not a full history of what the other party received.

If you use automated handover, check how it handles additions and corrections. You need to know what was newly sent and why; finding the same PDF again should not trigger another delivery.

If the same service repeatedly arrives late, adjust expectations or delivery. It may have a different billing date, incorrect contact address or require downloading. A one-off supplement resolves today's problem; understanding the cause simplifies next month.