Source authority hierarchy for corroboration. Tier 1 (highest weight): peer-reviewed papers, major news (NYT, WSJ), government sites, Wikipedia. Tier 2 (medium): Gartner, Forrester, IEEE, industry trade pubs, authoritative directories. Tier 3 (low): company blog, social media, general business sites. One tier-1 source > ten tier-3 sources in entity confidence calculation. Prioritize tier-1/2 in corroboration campaigns. Track source tier distribution quarterly. Degrading tier profile signals approaching confidence threshold failure. Minimum: 5 tier-1/2 sources per core claim.