I looked at all of your pictures.. All I see are circulation wear and tear marks. A Die Crack is a crack on the Die itself. When it strikes a blank planchet the metal will flow into the crack and form a raised crack on the coin.. not incused.
A die crack tends to protrude from the coin's surface because the metal literally forms an empty space where the metal is not compressed as much by the machine. Your pictures just show scratches for wear. (By the way, it is spelled nickEL, with the e BEFORE the l, just like the metal is spelled)
Yeah. Basically, the minting machine compresses the metal, and some parts are not as compressed, which forms devices (the bust, letters, etc.) which means that the metal is left a bit above everything else. So when the die cracks, it does the same that the parts that do not compress do... It leaves the metal there a bit above everything else, which is why it protrudes.
A crack on the surface of the die allows coin metal from the planchet to flow into the void created by the crack, thus, making it raised on the coin. Chris