Are those surely NATS codes? I've only seen the ",," endings in MetArt's system, which is not NATS.
If it's a NATS program, you can go to
http://NATSDOMAIN.com/internal.php?page=code_info and verify your link codes there.
With that said, I think it's a much better idea to improve your backend to support those link codes, than to edit them and gamble whether they will be tracked correctly or not.