This is definitely false. Relic WS do not increase in damage when used more than once.
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Honestly I'd say they should switch out the aftermath for something else. The +10 subtle blow doesn't do much when a lvl 90 mnk in full Empy Armor+2, Black Belt, and Rajas ring will have +40 subtle blow. Toss on an Auspice, and you hit the cap.