It's basically to ensure that the measure applies appropriately in a retroactive manner. If you look at this between 2012 and 2016, a risk score was required under the law for any sort of mission, whether it was a Canadian Armed Forces one or not. The legislation doesn't cover that in its current form for where the mission was designated by the Minister of Public Safety and Emergency Preparedness. It's just to provide assurance under the law that those missions are covered, both under the old regime, which required a certain risk score up to 2017, and from 2017 on, where the risk score isn't a factor.
On November 1st, 2018. See this statement in context.