Could you provide more information regarding the validation question. We had multi site application moved from CMS 11 to CMS 12. We had alternative domains created in integration and preproduction and like dev2.XXXXX.com / qa2.XXXXX.com .  Once the site has been validated in QA2 environment and are completely ready to cut over the domain, thats when we proceed with go live option as once you go live the CMS 11 instances gets removed after sometime (guess 10-15 days. not entirely sure about the timeline). After this we ensure that sites point to original domains as they were in CMS 11.

OK, now I understand what you did. I assumed I couldn't introduce new hostnames to the new project until the migration was complete. It would be nice if the documentation took mulit-sites into consideration and offered some suggestions.