Adrian Borland (specifically, the Honolulu Mountain Daffodils project, but also anything he did)
I saw Anna Russell in Carnegie Hall, back in the 60s or 70s. “I’m not making this up, you know!”
I only discovered Stevie Ray Vaughn about two months before he died. Should have gone to that show! 
I never heard anything by my favorite singer, Eva Cassidy, until after her death, despite the fact that she lived in the same county as me most of the last fifteen years of her life.
In fact, more precisely, I never heard anything by her until four and a half years after her death.