I was digging around on the forums for previous experiences, I came across one that had her package returned last March due to missing information but CIC also made mention that the Checklist had been updated on February 14th. At that time they advised her they were taking previous forms until March 15th. So maybe they do give a few weeks?
I know it's not for sure that they give a grace period but I admit it's the tiniest bit reassuring. In any case anyone sending as of this week please make sure to check the forms and submit the correct ones. Luckily you have the chance to correct that unlike some of us that sent early on this month