OVERFLOW and PIRACY

"Drainage younger that uplift or most recent exposure of the bedrock high"

  A set of diagrams below illustrate both the overflow and piracy mechanisms.  In both cases, the drainage must postdate uplift or most recent exposure of the bedrock high.  This is NOT evidence you find in the field.  But if the other criteria or evidence indicate the drainage postdates uplift or most recent exposure of the bedrock high, the only two possible mechanisms are overflow and piracy.