If you're counting the caffiene in chocolate, you are way way way overthinking all of this.
You'd have to eat a KILO of milk chocolate to hit 200mg, (its approx 20mg per 100grams) which is btw already a totally random low amount of caffiene as a daily limit anyway.
A mars bar is 58g total, milk chocolate makes up 40%. So 23g of milk chocolate is.....what, about 5mg?
If you ate enough mars bars to have caffiene problems, you'd be in a diabetic coma. Do you eat 40 mars bars a day?
In other words STOP the crazy!