Justice Ginsburg and citation to post-oral argument work

In her dissent in Shelby County v. Holder, Justice Ginsburg cites a piece about racial polarization that appeared in the Harvard Law Review Forum (p. 21).

I couldn't help but notice that the article was published after  the oral argument in Shelby County: a draft was released the week of oral argument (which took place February 27, 2013), and the final product published at the Harvard Law Review Forum April 27, 2013.

I then recalled that Justice Ginsburg cited post-oral argument work in National Federation of Independent Business v. Sebelius , last term.  There, argument took place March 27 & 28, 2012. But she cites a blog post by Ezra Klein published May 7, 2012 (p. 7).

I don't know if it's common for the Supreme Court to cite to post-oral argument work (although it's certainly common for the Court to cite to its own post-oral argument opinions), but the fact that I recalled these two instances, and that both by the same justice, struck me as (perhaps) noteworthy.