38 CFR 8.31: Total disability for twenty years or more.

Where the Disability Insurance Claims activity has made a finding of total disability for insurance purposes and it is found that such disability remained continuously in effect for 20 or more years, the finding will not be discontinued thereafter, except upon a showing that such a determination was based on fraud. The 20-year period will be computed from the date the continuous total disability commenced, as determined by the Disability Insurance Claims activity.