Printed abilities are the only ones that are counted for cards like this Lost Soul (or Herod's Dungeon, etc.) that reference abilities. The only things that can modify that number are increase/decrease special abilities. For example, if you play The Testimony (Hero gains 7 ability points) on Joseph (2/2) and choose to increase him by 4/3, he would then be 6/5 and be able to rescue the /4 or greater Soul. However, just playing a 4/3 enhancement on Joseph would not allow him access to the Soul.
