Google might be able to get away with it by claiming that they assumed that the documents sent to them where legal. Of cause if a judge decides that that is not a valid excuse than Google has a legal break on all DMCA take down notices, as they will have to take each before a judge to check that it's legal. If the judge agrees that Google's defence is valid there are two options.
1) The judge still allows the case against Google, but allows Google to use all the facts of the case to recover costs against the issuing party.
2) The judge moves that Google is not a party to the suit and says that the Injured party should sue the issuer,.