Pretty odd for IRS to accept an incorrect SSN on a return, it would have needed to belong to someone else with the same first 4 letters of their last name (I guess if its a common last name, it can happen)....

Im not sure an amended return would do anything for this situation.  I think you may be stuck waiting to see if IRS sends any notice about it.

This is why its so important for the client to review the return prior to filing, and they should always  verify the name and SSN is correct on the 8879.