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fkwOne is intentional and the other usually is accidental and part of normal wear.
Trimming involves intentionally altering the full length or width of the card, corner damage is different and can happen to any card that was not protected for 75+ years.
Many sets are so delicate with brittle stock that the corners will just break and fall off sometimes, ie. T222, T200, E145-1, W512, etc.