From my constant interactions with apple central, apple austin, store managers, and some knowledge of the team working on this (I don't work there, just pay close attention to everything they have said to me)....this seems inline with what I have heard...I posted this theory last night:
They realized they had a problem and attempted to find a solution. When they found out they could pull stock they started reserving the walk in phones for us. They know most customers do not need all the time allotted for their trade in. They can't plug us into time slots that are taken so they started telling us "just show up" knowing that eventually they would get stock that others could reserve normally. They then could not link our accounts directly, so they used the SN IMEI info as our reserved slot. They began work on a launch day add on to their system that would allow them not only to look up if we were eligible, but also if we had a phone reserved through this emergency reservation system. Finally, they did not want to tell the store managers too much till the system was better in place so they wont know the full story till Thursday night. As the calls and in person visits to the stores have been happening over the last 4 days, it seemed the knowledge base and plan was becoming greater and more organized.