When I was an investigator for Pinkerton, we did not even hire a security guard without checking his or her background - employment, neighbourhood, criminal records and more - for a ten year period. And Quebec Immigration will only require a three year background check of "the province's immigration law" on their future immigration consultants.
When I applied for employment with the Government of Canada, the R.C.M.P. did a thorough check of my background before granting even first level entry.
Three years is nothing in a person's history. The applicant may have committed murder four years ago and would still pass Quebec Immigration's new test.