The numbering of the classrooms within a building seemed random. For example, Royce 162 is next door to Royce 190. 163-189 don't exist. These rooms were pretty small, so it is unlikely that they would be split into 30 smaller classrooms. Similar story with the 3 massive lecture halls in the chemistry building (Young Hall, but not named after me): CS24, CS50, and CS76. Why weren't these named CS1, CS2, and CS3? But that confusion only lasts a day or two.