Just got off phone with passholder services and am now signed up for one of the additional dates. Those of you like me who tried and failed to sign up due to website and phone issues--and who took the time to contact Disney regarding your experience--can likely expect a phone call like mine. Don't give up hope! I just hope that the new dates work with your schedules.
The CM was very apologetic and nice and explained the available dates and options. He asked me not to share the additional dates so that those like me who were shut out and contacted Disney about it would get first opportunity, and I will honor that--so don't bother asking. I expect these days will be published by Disney by middle of this week anyway, if their previous mea culpa was accurate.
Disney can absolutely mess up. But this will go down as another experience for me where they did everything reasonable to make it right again.