Yes over written data can be recovered even after its been deleted, formatted and written back over again. There is software out there that can reconstruct a file by what bits are recovered of the hard drive that is if there is enough of them. The other way data is recovered is by removing the plates and then read with some other high dollar machine. The Goverment has software that will format the drive and write to it like 7 times first with all 1s and the with all 0s. that way the disk has been completely written over.