Files that do not open are corrupted. The deleted files have either already been overwritten to some extent with other files or they could not be correctly reassembled. Corrupted files which were recovered from an NTFS drive have at least been partially overwritten. Corrupted FAT files have either been at least partially overwritten or could not be correctly reassembled.
Though Recover4all displays recovery chances to the best of its knowledge, even files with "good" recovery chances can turn out to be corrupted. Consider for instance the following scenario: if the 1st file is deleted and then partially overwritten with a 2nd file, the 1st file is unrecoverable and will not be listed in Recover4all. But if the 2nd file is then later also deleted, the disk space of the 1st file can appear to be free again and Recover4all might assume that it is recoverable and list it.
To get an idea of what the recovered files consist of and to see with how much and what kind of data they were overwritten with, you can open them in a text editor or a hex editor. For files that contained some plain text, you might this way even be able to retrieve some text from the corrupted file.
For very precious files that turned out to be corrupted after recovery, manual recovery by a professional data recovery service with a laboratory and special equipment can be an option.