We are integrating Magento with an existing system. Our existing system already has order numbers. There has been a lot of confusion since Magento has its own order numbers, and our existing system has different order numbers, so we're trying to get the order numbers to match up.
I have an observer set up for sales_order_place_after where I get the order number from our existing system. It doesn't seem to work to $order->setIncrementId($our_existing_order_id) I don't know if this is really all that good of an idea anyways..
Really, the end goal we want is for the order #s in email receipts that are sent out to match the order #s in our existing systems. Is there a better way to make that happen?