In addition to sbm12's helpful interpretation of the fare rules page, I have also noticed that for an AC fare I am booking today, after I clicked through on the AC site to the page with the Review of details, Itinerary & Quote, the fare class appears below the fare description (i.e., Tango, Tango Plus etc.), and the fare class corresponds to the class that sbm12 indicated on the rules page.

I am booking fare classes are M & Q (both Tango Plus), which are designated to earn OP miles.