In 2003 OWCP migrated from maintaining paper files to an electronic imaged system. When there is no activity for an extended period, paper files are shipped off to the federal record center. The federal record center destroys files after 15 years. If you have an older claim that was a paper file that has been "retired" to the federal record center, you are at risk of your paper file being destroyed.
This means if you had an old knee injury, and now need a knee replacement, you may have difficulty getting that procedure approved if the file was destroyed due to the file retention policy. If you have an older paper claim file, and do not have a complete copy of your file, you should write OWCP and request a copy before its too late.