Hi! This is my first time playing the game and I have a question about the evolution system.

So I was trying to get Gabumon black cause that's a line I really like and I'm wondering if the evolution system is based on stats, how did i not get gabumon black? I had 3 different stats matching for him and somehow still got ClearAgumon. Is there a more sure way to get the ones you want or is it more stat points and gamble?