Battle damage arithmetic

I've seen several fights where the damage to the enemy does not match to their health.  Sometimes I've seen the enemy die although the amount of declared damage is not high enough.  
In this fight, I've paused while the opponent is still alive and you can see the discrepancy.

Damage done through round 5:  
     round 4 -  24+2+3 = 29
     round 5 -  32+6+5 = 43
    Total damage = 72;  villain should have 28/100 life but has 23:
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Actual Filthy villain stats after round 5:

Type: Criminal
Life: 23 / 100
Initiative: 10
Hitting: 10
Damage: 2 - 6
Protection: 5%
Weakness: Slashing
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In round 6 the villain was killed with a 24 damage attack.
  


Round 1

- You moved closer toward the Filthy Villain!
- You moved closer toward the Filthy Villain!
- The Filthy Villain moves one step closer to you!

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Round 2

- You moved closer toward the Filthy Villain!
- You moved closer toward the Filthy Villain!
- The Filthy Villain moves one step closer to you!

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Round 3

- You stand your ground! Your protection increased by 25%!
- The Filthy Villain moves one step closer to you!

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Round 4

- You did 24 damage to the Filthy Villain!
- Blitzen bites at the Filthy Villain but failed to cause any damage!
- Brute Mercenary attacks the Filthy Villain dealing 2 damage!
- Personal Bodyguard attacks the Filthy Villain dealing 3 damage!
- You moved further away from the Filthy Villain!
- The Filthy Villain moves one step closer to you!

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Round 5

- You did 32 damage to the Filthy Villain!
- Blitzen charged against the Filthy Villain dealing 6 damage!
- Brute Mercenary attacks the Filthy Villain dealing 5 damage!
- Personal Bodyguard attacks the Filthy Villain but failed to deal any damage!

Round 6:
Round 6

- You did 24 damage to the Filthy Villain!

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You are Victorious!