Probably half the things you like today were "fusion" dishes when they were introduced 100, 200, 500 years ago. Where's the cutoff point where before date X it

Probably half the things you like today were "fusion" dishes when they were introduced 100, 200, 500 years ago. Where's the cutoff point where before date X it's not fusion and after date X it is? There's a long list of foods that are common now but didn't exist until some culture started using ingredients and techniques they learned from another and fusing it with their own recipes.