I will bring up the idea of an invoice having the option to be added automatically to the Registry, but I foresee a bunch of problems. Books that aren't in the Registry yet, books that get sold immediately, upgrading a slot to the better book, etc.... it sounds like a programming nightmare and something that would add yet another hurdle to an already shaky database. I'm still trying to get the scoring update on solid ground to start making changes. I don't mean to sound pessimistic, there's always a chance, but if we were to ever look into it, it would be years down the road.
The Certification Number is on every invoice already, you just didn't realize. A certification number is the invoice number and the the line number... So the second book on invoice 123456 would be 123456002.
I hope this helps.
Best-