I've got 10 pairs of 18650 (20 total). Most are newer-ish, but a couple pairs date back to 2014. My oldest is a pair of purple Effest "35A", the ones everyone screamed "Don't Buy, they suck!". Those are still my daily travelers, backed up by a pair of equally-old Sony VTC4s. I'm amazed they've survived 3 years of daily use. They have far surpassed their expected number of charging cycles and continue to reliably fire my Fuchai 213. I'm actually expecting them to die soon, their power curve is becoming noticeably diminished. I still get a day out of them at 60 watts with juice to spare (most days).
I've yet to have an 18650 battery die on me, but I did give away a pair of VTC5's that were weak from day one, and sold a pair of Samsungs because my desperate friend begged me to.