Synonyms for Corroborative (same or very similar meaning)
WordNet sense 1 (serving to support or corroborate):
collateral, corroboratory, confirmative, confirmatory, confirming, substantiating, substantiative, validating, validatory, verificatory, verifying
WordNet sense 2 (furnishing support or assistance):
supportive
From the ODE community, based on WordNet
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