Worse, if they knew about this problem, the rational response would be for them to flood the court with individual lawsuits, despite the pendency of a proposed class action to which they would belong if it were certified.
It looks messy. Wasteful. Better to give them a shot to wait it out, and file only if it turns out to be necessary.
Thus, class action tolling.
The Effect of Tolling
A medical malpractice article misleadingly suggests (The Class Stops the Clock) that the effect of tolling is to "suspend" the running of the clock. Perhaps it is to be forgiven (and it's a really good article, most ways, detailing the origin of the doctrine in the 1973 Supreme Court case American Pipe v. Utah; see especially its nice discussion of the trap for the unwary in the majority rule that an absent class member who files her complaint before the class certification is decided does not benefit from tolling).
But the rule is not at all that time stops for purpose of the statute of limitations when the complaint is filed, and starts running again when certification is denied or the class is decertified.
No, Chardon v Fumero Soto (1983) establishes that a court must consult the substantive law's tolling provision, if there is one, and that under certain circumstances an entirely new statutory period may run. It depends if, as in American Pipe or Crown Cork & Seal v. Parker (1983) the statute indicates "suspend" (see section 5 of the Clayton Act for antitrust, for example) or if the statute, like the Puerto Rican savings provision in Chardon grants a new statutory period for the re-filing.
(A savings provision will allow a plaintiff, kicked out of court for a non-merits based reason [like jurisdiction, or the class action which included them failing on the basis of numerosity, typicality, or adequacy of representation] to refile within a certain length of time, despite the running of the statute of limitations between the time of filing and the dismissal of the claim.)
That is, one could be gravely incorrect if one assumed that the only possible result of application of tolling to an absent class member's individual claim would be that they would have the time they had remaining left in the statute of limitations when the complaint is filed "tacked on" to the moment of denial or decert.
Other reading
Evan previously blogged about Class Action Tolling at the Illinois Trial Practice Weblog.
Prof. Rhonda Wasserman of University of Pittsburgh School of Law has written about tolling in successive class actions, or what I believe is called the "anti-stacking" rule.