Yes. It is not necessary for you to retain ownership of stock in the company after the class period to participate in the class action lawsuit.
The primary requirement to join a securities class action is that you either bought or sold stock during the class action period and sustained damages. The class action period is the isolated period of time in which the prices of shares where inflated due to the false information presented by the publicly-held company. Additionally, in order to participate in the class action, you cannot have filed your own lawsuit against the company. If you have filed your own suit and would like to join the class action, your attorney will need to file a joinder request for you to be included in the class.
You might ask: which is better, joining a class action or filing my own lawsuit? Personally, I’ve always recommended filing your own lawsuit if you have the funds. The reason for this is simple, the more members of a class action, the less money each particular member will receive from the class action. There’s a saying in the legal community that the only people who truly benefit from a class action are the lawyers, as the largest chunk of money tends to go directly to them.
If you are concerned that you won't be a part of a class, the best means of proving you sustained damages during that time is to show your share certificates from during the class period. As long as the certificates prove that damages were sustained from the purchase or sale of shares, then you are a member of the class. If you simply broke even--did not sustain any immediate losses--then you do not have any grounds to be a part of the class. If you are unsure whether you qualify as a class member in a securities class action, consult with an attorney.