“Pursuant to Michel v. Graydon, 2020 SCC 24, child support can be recalculated retroactively even if a child has reached adulthood. In D.B.S. v. S.R.G., 2006 SCC 37, the Supreme Court of Canada interpreted s. 15.1 of the Divorce Act, R.S.C. 1985, c.3 (2nd Supp.), as precluding a court from granting an order on an original application for retroactive child support unless the child beneficiary is a “child of the marriage”, as defined in the Divorce Act, when the application is made (para. [2]). After D.B.S., courts grappled with whether the same principle applies to provincial legislative schemes or to variation applications under s. 17 of the Divorce Act. In Michel v. Graydon, supra, the court confirmed that D.B.S. does not stand for the proposition that courts can retroactively vary child support only while the child beneficiary is a “child of the marriage” (at para [15]).”