Carl,
I am sorry that I can't help with the IATA-3 thing. I hope someone more knowledgable than me will chime in.
I posted because I wanted to "welcome" you to the wonderful world of stop-overs. They are GREAT as long as you are doing them voluntarily. (Not like the folks on the diverted UA flight today).
I hope you end up somewhere fun with your stopover and get two trips for the price of one.
Best regards,
-levi aka eastwest