Can a motion be brought on consent to add additional class members to a class action?

In Denis v. Bertrand & Frere Construction Co., [2002] O.J. No. 3419, a motion was brought on consent to add “additional class members”. The judge had previously granted certification and had ordered that class members “join” the class action by a certain date. (The decision granting certification was not provided.) Four people who failed to “join” the class brought a motion to be allowed to “join” late. In brief reasons the court granted the relief. The case offers no assistance in understanding the statutory authority and reasons for the initial order directing that class members “join” the class.