1 a (1) : of, relating to, or given to retrospection : based on memory <a retrospective report> b : being a retrospective <a retrospective exhibition>
2 : affecting things past : RETROACTIVE<retrospective laws>
3 : relating to or being a study (as of a disease) that starts with the present condition of a population of individuals and collects data about their past history to explain their present condition
In short, the word means acting, or an enaction on the present, taking into account something from the past. Of course, it means something completely different here in Australia, to what it may well mean in the United States english language lexicon. As Little Johnny Howler said today:
Interpret it as you will, reader. The intent is quite clear. Australia will do absolutely nothing to interfere with the American english dictionary, regardless of whether the life or mind of an Australian citizen is at stake. Let this be a lesson to those of you contemplating even thinking about becoming a soldier of fortune.