What is the state of the law around corroborating documentary evidence?

Finally, the agency reasonably concluded that Singh's documentary evidence did not rehabilitate his credibility. See Biao Yang v. Gonzales, 496 F.3d 268, 273 (2d Cir. 2007) ("An applicant's failure to corroborate his . . . testimony may bear on credibility, because the absence of corroboration in general makes an applicant unable to rehabilitate testimony that has already been called into question"). As discussed previously, the letters Singh submitted were inconsistent with his testimony regarding the dates of particular incidents and the duration of his hospital stays. Further, an additional letter from Singh's political party

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did not address, and thus did not corroborate, his allegations of past harm.