Hi KLiao,
It looks like the "9" got hit with something exactly there, without touching any other part of the design. One can see what's left of the curve, and the straight line looks like a ridge above the rest of the "9", i.e. above the loop.
It may sound unlikely that damage would be so "localized" and so neat but, to make a wild guess, it may happen to one in 3000 coins, and most of us look at 1000s and 1000s of coins in a year...
If the straight line is like a ridge, then it's clear it's PMD.
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