When I was in college, every Color Darkroom Dataguide came with a Shirley neg. I still have mine.
"I only wanted Uncle Vern standing by his new car (a Hudson) on a clear day. I got him and the car. I also got a bit of Aunt Mary's laundry, and Beau Jack, the dog, peeing on a fence, and a row of potted tuberous begonias on the porch and 78 trees and a million pebbles in the driveway and more. It's a generous medium, photography." -- Lee Friedlander
These negs were used to set the "slope" or to match your "unders" and "overs" to the normal negatives on older analog minilab printers. Later analog minilab printers didn't need them so they became redundant even before digital labs became the norm.
I believe that the Kodak facility in Melbourne had a "Shirley" set up for making these negatives. Last I heard they were trying to think up a reason to keep making these negs! Shirley has probably ended up in landfill somewhere.