I know from my mechanic days the fat from fingers and grease reacts with tungsten glass when heated to weaken the glass that's why your not to touch the glass on bulbs, i wonder if some chemical or the acid from wine etc starts the process off, or are there different forms of glass breakdown, if a batch of glass is bad why be in certain places and not others it makes no sense it should be widespread not localised. If it was damp then why are bottles buried or found in rivers not effected, i reckon it has something to do with light and heat like the tungsten bulb theory.
Your bottle John do you think could be bad on one side due to it's position in light maybe sat on a shelf for years without moving?.