The routine above picks a set with (A + C) AND $07, multiplies by three, and copies the three bytes into the room bytes of ACG_KEY_PARTS, stepping by eight -- which is +$01 of three consecutive object records in INITIAL_STATE, the field that says which room the object is in. So this chooses where the three pieces are hidden, and it does it by editing the template before LOAD_INITIAL_STATE copies it.

Every one of the 24 values is a valid room number, 149 or less, which is what a table of rooms should look like and what a table of anything else almost certainly would not.