One of the students in BUSINESS 101 noticed that in a reference such as (Oram, 2007; 2011) I was using colons, instead of commas. They said it should be (Oram, 2007, 2011). I was away from the office (without a copy of the Publication manual of the APA to hand), and I said it might just be a difference between the 5th and 6th editions. Being a long-time user of Zotero (and before that Endnote), I have stopped worrying about how my citations look. I take it for granted that they are correct.
I was wrong. It should have been (Oram, 2007, 2011).
So, thanks to the student (whose name I no longer have) for pointing that out.