I had some YoZuri copolymer delaminate on me a few years ago while fighting a Jack Crevalle. I think the innner nylon stretched more than the fluorocarbon would and the outer coating came off. I don't think I was anywhere near the 20 lbs of the line test it was just a long fight on spinning tackle and the line stretched. The nylon still held and I caught the fish after easing up on the drag, but it was a mess with the outer layer peeling off.