After discussing the use of ClaimReview with fact-checkers, there is confusion among the fact-checkers about how to populate the field for SameAs field. Some fact-checkers have been using for the URL of speeches or articles where the claim appeared to provide evidence and details of the claim; others have been using it for the home page/knowledge base article on the person or entity that made the statement.

Both have value for search engines and other uses. It’s valuable to be able to see a knowledge base article on the person or entity being checked; it’s also valuable to be able to see where a false claim was published, particularly the article or speech where the claim originated.

The solution: We propose that:
sameAs will continue to be used for the entity or speaker that made the the claim (we called it the “who to blame” field). This field would typically be the home page of the person making the claim, or their Wikipedia page.

We will add a field(s), under ClaimReview, called claimUrlOriginal of type URL to designate the URL of the origin of a claim such as a speech or article; fact-checkers could include additional URLs (claimUrl) of type URL if the claim has been repeated in other publications.

For example, here is a fact-check by PolitiFact of a claim by New Century Times. The SameAs field is the website’s URL. The claimURLOriginal field would be the article that contained the claim that was fact-checked. That claim also appeared on Vote.us.org, which is listed as a claimURL.

{
  "@context": "http://schema.org",
  "@type": "ClaimReview",
  "datePublished": "2018-01-05",
  "url": "http://www.politifact.com/punditfact/statements/2018/jan/05/new-century-times/white-house-staffers-removed-job-subject-false/",
  "claimReviewed": "Breaking: FBI just raided the White House, 6 people thrown out.",
  "claimUrlOriginal": "http://info.nct.news/2017/12/30/breaking-fbi-just-raided-the-white-house-high-ranking-officials-thrown-out/",
  "claimUrl": ["https://www.vote.us.org/memo/thread/3419/fbi-just-raided-the-white-house-6-people-thrown-out/"],
  "author":
  {
    "@type": "Organization",
    "name": "PolitiFact",
    "url": "http://www.politifact.com"
  },
  "itemReviewed":
  {
    "@type": "CreativeWork",
    "author":
    {
      "@type": "Person",
      "name": "New Century Times",
      "jobTitle": "website",
      "sameAs": "http://newcenturytimes.com/"
    },
    "datePublished": "2017-12-30"
  },
  "reviewRating":
  {
    "@type": "Rating",
    "ratingValue": "2",
    "bestRating": "7",
    "worstRating": "1",
    "alternateName": "False"
  }
}

Edited 2018-01-23 by @danbri to highlight key terms, omit HTML script tag, improve formatting.