For external systems, is there a way for them to generate an empty sales order (to get the id and tranId), and then later fill it in? We're getting duplicate sales order ids (from users) so we need to turn off the ability for them to override the transaction id while allowing the external systems to either A) Pass in their own SO or B) Quickly get an SO Id and then later fill out the SO.

I don’t think so. Could you add a dummy item that is always removed later?

Sad. Nah, would be too much of a pain

Auto-Generated Document Numbers goes over how to prevent duplicate tranids

We generate unique externalIds (using a unique identifier in the external system) and let NS deal with the tranid automatically