Research reports published on the webpage of the home institution are sometimes updated during the revision process. Suppose a first version was published in 2013, and the update came in 2014, and suppose the first version is not available anymore. The web page may say something like "XYZ, 2013. Revised 2014". Which date to use for citation?
"2013": This may please the sensitive among the authors.
"2014": This is factually correct as I'm citing the content of this version which is also currently online. But what if they update again?
"2013. Revised 2014": This has its obvious benefits, but is probably too cumbersome to be consistently implemented.