TL;DR
A rating in continuous effect for 20+ years is locked in for life — VA cannot reduce below the lowest rating held during that period.
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The 20-year rule (rating protection)
Key concept. Under 38 CFR § 3.951, a rating that has been continuously in effect for 20 years or more cannot be reduced below the lowest rating in effect during those 20 years. Once you cross 20 years at a given rating, that rating is locked in for life.
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