I've got many thousands of miles on GP4000s...I can count the number of flats I've had on my hands. Never had one that left a visible cut in the tire.
I did have ONE that caused me to pitch a tire a couple years ago. I slammed into a pothole I'm surprised didnt taco my wheel. Tire developed a slight lateral bulge in one spot...pretty sure I snapped a couple threads on the inside. Was still perfectly rideable. Took a week to even notice I had a slight wobble.
I still cant figure out how people are getting sidewall cuts on roads. Road tires are intentionally designed with thin, flexible sidewalls. Thats what makes them both faster and more comfortable.