I am curious.  I have just replaced 17 of 34 Anderson windows in a large sun room.  All manufactured in 1991.  The company could not have been more accomdating.  They listened, told me after the first two went smoky, how to review the others for possible problems.  I used a straight 24″ aluminum bar to lay across the glass and measure any depression in the mid of the glass.  That is how I found the others.  They had gaps of 3/8 to 1/2″.  I called them back with my findings and they sent all windows drop ship at no cost.  It is a job replacing them 10′ high though.  Anybody have a similar experience?