I've had a couple go bad on me, many of us probably have had that experience.  I had a Woodhaven Crystal go flat after a year.  Woodhaven made that right and sent me an autographed, hand selected replacement.
But I was digging through my box of calls and found a real gem this spring.  It was put in the box of calls that didn't make the cut a couple of years ago.  This year, it sounded like turkey music.  As the glue and wood dries and ages can they actually get better, or did I just overlook this call before?