I am working with someone who wants to re-use sales order numbers if an order was cancelled. I think this is a bad idea. I have found invoices that were linked to a cancelled order and that person did not change the information on the bill. It lead me back to a different customer. I was taught to void the sales order if it was not carried out.
You would Close the SO that is not needed, either the specific items if it is partially fulfilled, or the entire SO, that is no longer needed. There is no reason to reuse Numbers; let QB just keep numbering sequentially. There is no need to manually force that process along. It's just a tracking mechanism. There is no VOID; an SO is Nonposting and never affects the financial data. It is a Fulfillment Management tool. If they ever invoice from an SO, then the order by definition was fulfilled, not Canceled. What happened is, it seems to have been returned or rejected, not canceled. The Invoice is proof that the Sale happened.