Rose from UPitt told us that they try to fill half their seats with the first wave and the other half with the 2nd. They do 6 interview dates total, so from the first 3 dates (~150 people) they accept about 80 to fill 40 seats. Same with the 2nd 3 dates, hope this helps for anyways applying to Pitt
Most public schools will have good percentage of class will be filled becasue most people with Instate acceptace will decide to go to their state schools. However with Private schools like BU, NYU, TUfts etc... would have many seats open becasue most people who got accepted to those schools also got accpeted at other places and they will choose a low cost school over them. This is just pure speculation.