Special modifiers are bonuses found on such items as Uniques, Rune Words, and Set Items, but not on Magical or Rare Items. They are not like prefixes or suffixes. These bonuses are picked from a pre-set list, not randomly-generated, and not randomly valued either. There aren't multiple types or levels of Crushing Blow, or Ignores Target's Defense; it's there or it's not, to whatever value is preset.