How much can I omit in Author-Date citations?

I’m using author-date citations for an academic journal article. (It’s a humanities article, but they prefer author-date, with which I am not very familiar.) I’ve got it all figured out, except one thing: if I refer to only one work by a given author (Joe Smith, say), then do I still have to include the publication year in my parenthetical citations? Here’s an example:

Indeed, Joe Smith has recently claimed that “Fluther is awesome” (2008: 27).

Obviously, “27” refers to the page number. But if there’s only one work by Joe Smith that I reference in the whole article, do I really have to put “2008” in the parenthetical citation? Doesn’t the ostensible function of the publication year, that of differentiating between publications by the same author, become unnecessary when I refer to only one work by this author?

I ask because there are authors with only one work that I refer to, so the inclusion of years looks clunky. Further, if it really is better form to include the year even when it has no real function, do I have to include the year in every parenthetical citation? Even if it’s just a citation noting that the latest quote comes from a different page? Like this:

Indeed, Joe Smith has recently claimed that “Fluther is awesome” (2008: 27). He goes on to aruge that “Fluther is the most amazing device known to mankind’ (2008: 29).

Presumably, I don’t need to 2008 there, right?!? Any help from people more familiar with the author-date system would be much appreciated. Thanks!!