What is "Slippage" in the world of Data Recovery?

Slippage is a condition within a logical volume in which extra sectors are present. There are many reasons for slippage, but it all comes down to loss of information stored in the P-list module within the track -1 area of a hard disk drive. This presents a critical problem since a FAT table, NTFS MFT record, directory fork, or other file map does not line up with the correct data. Almost all, if not every single file will appear corrupted on a volume with slippage. Slippage can only be corrected by removing the bad sectors, or the equivalent number of sectors in the approximate area where the extra sectors are located. Manually correcting slippage can be an extremely time consuming and frustrating process, involving complex calculations and lengthy searching for file headers. Fortunately if the "P-list" can be recovered from the bad drive, the exact location of the bad sectors is known, and the problem can be corrected in a matter of minutes.