You’re right, it looks like a ‘nibble’ out of the extreme edge. In practice, it quite conceivable in a domestic setting that somebody has walked past with something perhaps long and pointy - a telescopic tube from a vacuum cleaner, and curtain rod, an umbrella, could be almost anything. It catches the edge of the tweeter, and dents the outer area on the way past, with barely a tap noise.
I appreciate your perspective. I spent most of the night looking through various American sites and gathering information. These images, comprehend the appearance of a blown LS50 driver. The comparison is vastly different from my driver, which I'm putting down to a durability issue. The amplifier is not the culprit in this case.