Was the original file system FAT32? If so, then your files are probably corrupted because the file system was fragmented.
FAT32 keeps a record of all the clusters that make up a file in the File Access Table (FAT). The formatting process writes zeros to both copies of the FAT, thereby making recovery of fragmented files very difficult, if not impossible. Data recovery software can find the name of the file, its size and its starting cluster, but it can then only assume that the file is contiguous. This means that the first fragment of a fragmented file will be OK, but later fragments will come from somewhere else.