Just checked - mine are 8/9/2013.
I wonder if mine have held up since I haven't tried alternate different filters - I'm still using the defaults. I've simply tried different tips. Could the early production runs be fragile enough in some respect that changing filters is more likely to result in some kind of failure?
My impression is that the most common failure has been the loss of sound in one of the ear pieces? There's been mention of "phase" issues in early production runs. What would be the symptom?
I've changed the filters a few times, but not many. Not sure about the phase issues though.