What is the test for adding plaintiffs to a proposed class action where the named and proposed representative plaintiff has no legitimate cause of action?

The matter of adding plaintiffs to a proposed class action, where it subsequently turns out that the named and proposed representative plaintiff has no legitimate cause of action, was dealt with in Ontario in the case of Segnitz v. Royal & Sun Alliance Insurance Co. of Canada (2003), 2003 CanLII 64297 (ON SC), 66 O.R. (3d) 238, 40 C.P.C. (5th) 140 (S.C.J.), which presents a similar scenario to the case at bar. That case involved a proposed class action against a group of insurers who paid the value of salvage for vehicles after deducting the deductible amount. The plaintiffs claimed that if the insurer exercised the option of taking possession of a vehicle for salvage, it should be required to pay the insured the entire value of the vehicle without subtracting the deductible.