Typically, the room block for the nights preceeding and after are lower than during the actual conference week.
For example if the room block for the week is 250 rooms/night, the nights before gradually increase 15/50/100 (Thur/Fir/Sat) and the opposite at the end of the conference. I'm not sure what block size Angel has set up for Sat, but if enough people are taking the cert test on sunday along with others who want to do the extra things on sunday (motorcycle ride, cowboy shoot) they could be filled.
Hopefully it can be fixed so more people can get the conference rate on Sat.