In the FB case, advertisers have gotten what they paid for as per contract. The metrics concerned stuff that's not in the sales contract but which FB used to su

In the FB case, advertisers have gotten what they paid for as per contract. The metrics concerned stuff that's not in the sales contract but which FB used to suggest their ad inventory was superior vs. what it actually was. So you're unlikely to see any lawsuits - not worth anyone's while. You will very likely see FB being pressured to open up to more third party validation of what they claim about their ad inventory at least for big advertizers who put in 10s of millions of dollars into FB advertising.