How to cite an updated report? 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?

Argument for

"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.
I think the main problem here is the use of the term "published" just because it is posted on the web page. If a report is under revision, it is strictly speaking not published. Once published it should be fixed in terms of its content or it should carry some form of revision marking such as "Second Edition" or "version 2" in which case the different editions or versions must be continually available. 

If you find some information in the 2013 draft which is later dropped, it means the authors no longer support that point for one or another reason. Hence it would be potentially bad to attribute such a point the authors.

So from this perspective I do not support any of your forms for referencing. It appears you should view the work as unpublished and only rely on the latest version as a source for information.