In my related works section of the paper I am writing, there are two papers by roughly the same group of authors. Paper A (2015), and Paper B (2014).
Paper B (2014) is based on Paper A (2015), and cites it as a unpublished work. But for some reason or another Paper B was published first. (Possibly because Paper A was a more significant work, so was targetted at a better venue with a longer review time, whereas paper B was a relatively minor extension published as a relatively unknown workshop.)
I'm only briefly discussing them in my related literature section. Do I need to call attention to the fact that Paper B is based on Paper A, even though the dates don't line up.
I currently have something like:
Paper A (2015) prepared the dataset using methods Foo. This dataset was uses in the evaluation of the models of Paper A (2015) and Paper B (2014) which were based on the principle of Bar. Paper B (2014) extends Paper A (2015) by adding support for Buzz.