The  Sweet Victory achievement follows your all-time trophy record since you started playing. It does not include all the trophies you ever gained, only the highest trophy count you have achieved.

For example:

• Your all-time high is 1000 trophies (Sweet Victory shows '1000')
  
• You then lose 20 trophies in a battle, which brings your current trophy count to 980 (Sweet Victory still shows '1000', because it's still your all-time high)
  
• You then win 15 trophies, and your trophy count increase to 995  (Sweet Victory still shows '1000', because it's still your all-time high)
  
• Next, you win 25 trophies, and your trophy count rises to 1020 trophies (Sweet Victory now shows '1020', because this is your new all-time high)
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