Reviewing response to the record breaking late frosts

Frost tolerance this spring was surprising. Some vines ignored frost, others were lost all their flowers and/or fruit to frost. Here is a recap (click to enlarge). The data is in roughly chronological order. The blue lines represent  frosty mornings.

To summarize, it looks like the local wild varieties have adaptations that maintain fruit production despite a late frost, even a record breaking late frost like those we suffered through in 2013.  I've been told April 15 is the last possible frost date, and we had 2 after April 15.  The French-American crosses have no coping adaptations, and none produced any fruit.  The North American bred vines, Extra and Lenoir were in between.