My assumption is that a law firm would not file a case without passing a stat sig analysis.
Most smaller firms don't have skilled analysts or the right tools and understanding to even think about an event study before filing a complaint. They simply look at the dollar drop and assume damages.
An outside expert is expensive and usually only employed once a law firm(s) wins lead plaintiff and need to file an amended and consolidated complaint.
I have seen many shots in dark that won't pass the defendant expert analysis or mine.
Frequently these lawsuits are filed and never intended to go to trial. The law firm wants to settle and collect a fee. The companies choose to settle because it is cheaper than going to court. It is a form of legal extortion. Some cases are obviously real, many others legal extortion.