Correct me if i'm wrong but i was getting impression that for every event there is an achivement for completing it.

I was doing my 15th or so run in Dahlgur Oasis, Act 2 (hunting for Bashiok) and suddenly there is this lever that drains water from a little pool and there is entrance to the Tomb of Sardar.

http://i.imgur.com/Ds5Nx.jpg

You go in, then "New Event" animation pops up, you complete it, but you get no achievement (because there is no achievement for completing this event on the list 'Campaign -> Act 2').

Someone forgot to add it or there are events without achievements?