The information in the link is helpful for retroactive changes for a child who may or may not have been a child of the marriage, not for children who are entitled to support. It's a change to support applications for a child who is not eligible for support.
Of note:
The Supreme Court of Canada has now clarified that a parent cannot bring an original application for retroactive support under the Divorce Act if the child was independent and over the age of 19 at the time the application was made. However, a parent may bring an application to vary support for an adult child under the Divorce Act, as long as the adult child remains financially dependent. Either an original application for support of an adult child or an application to vary an existing child support order, can be made under the Parenting and Support Act.
This is the only element of the article/case law that has been updated. Should also note that the read of the supreme court case clearly outlines that the court has the discretion to determine if a retroactive award would be harmful or unfair. In Trix's case, his ex would more than likely argue it would be unfair to make her pay back thousands in support she wasn't entitled to.
Both the article linked and the cases clearly note that changes to income, child support amounts and eligibility for adult children should be handled as soon as possible to avoid any issues and notably that child support is the right of the child.
Also of note from Michael v. Graydon:
the date of retroactivity should perhaps correspond to the date when the support ought to have been paid. Effective notice to the payor parent, the default date to which a child support award should be retroactive, is a broad concept which goes well beyond actual knowledge of a filed variation application.
Most importantly though across all of the info linked--blameworthy conduct is noted as needing to be avoided at all costs. As in, make sure you advise the payor when a child is no longer entitled to support; make sure you advise the recipient when your income changes and update accordingly; and, make sure you have full disclosure and all relevant information to avoid blameworthy conduct.
For this specific case with Trix, his oldest is leaving for school and therefore is entitled to "summer only" support as of September. His younger daughter is either living with him full time or they have shared custody. In which case support for her requires updating. To avoid arrears building up for full table for two kids, best to file now.
I will state again that FRO is a different beast when it comes to support cases. It's best to file quickly to get the matter changed as it takes several months (or years) to update. A friend had a case moving quickly pre-pandemic, it was held up for a year in 2020, finally had trial in early 2022 and now he has to clear significant arrears accumulated with FRO.
