Don't know how you found that, but I agree it's shocking that the companies weren't sued or investigated by the SEC for not releasing what's clearly material info - it doesn't get more material than a CRL! Actually, maybe some were - you'd have to find the 18% who didn't PR the CRL and google them for lawsuits - the paper doesn't give names, and the paper only looked at the time period from 2009-2013, would be tough to find such old news.
Found this article - FDA can't release contents of CRLs, only companies can, and the authors of your BMJ study worked for the FDA so they had access to them - they also say CRLs are material info and SEC requires PR for them: