"Human Rights Watch, a pressure group, recently revisited the social-media evidence it had cited in its public reports between 2007 and 2020 (though most were published in the past five years). It found that 11% of it had vanished. Others have run into similar problems. The Syrian Archive, a non-profit group that records and analyses evidence of atrocities in Syria, estimates that 21% of the nearly 1.75m YouTube videos it had catalogued up to June 2020 are no longer available. Almost 12% of the 1m or so tweets it logged have also disappeared."