There's no proof that Clarence Thomas would have been denied admission to Yale were it not for the existing racial preferences; in other words, there's no proof that Clarence Thomas actually benefitted from the quotas policy at the time. Clarence Thomas has been consistent: He supports defining Affirmative Action as making sure to find already-qualified minorities; he has consistently opposed lowering standards to accept minorities. "'The effort on the part of Yale during my years there was to reach out and open its doors to minorities whom it felt were qualified,' Thomas testified. 'I took them at their word on that, and I have advocated that very kind of affirmative action.'" https://www.mirror.co.uk/news/us-news/justice-clarence-thomas-benefitted-affirmative-30355926

At Yale, before racial quotas were implemented in the early 1970s, the class entering in 1966 graduating in 1970 was 3% African American. (http://archives.yalealumnimagazine.com/issues/2011_05/feature_howell.html) In 1984, about 15 years after racial quotas were implemented, 6% of the class was African American. (https://oir.yale.edu/sites/default/files/pierson_update_1976-2000.pdf page 15). Thus, there’s a far more than 50% chance that Clarence Thomas would have been admitted anyway even without minimum racial quotas.