What you likely know is what the cacao percentage number tells you on dark chocolate. So if you have a 70% bar the difference up to 100% is sugar in a classic instance, whichever sugar or sweetener it is.
For a 70% it would be 30% sugar in the bar. A 84% chocolate will have 16% of sugar, a 55% will have shocking 45% sugar – almost half a bar is sugar in this case. Cacao content tells you about sugar content.
-------------
What you may not know is that an 85% from one brand can be very different in true potency and flavor to another brand. Because the percentage of cacao no matter if it's 70% or 85% counts for the total cacao percentage - which includes also cacao butter.
Cacao butter is not detrimental for you but the antioxidants and benefits are in the solids and in the beans before separation of butter/solids. A lot of big brands who use lower grade cacao compared to Antidote or other specialty brands have likely more extra fats added. Meaning in order to make the cacao more palatable, extra cacao butter is added to stretch the flavor resulting in a more creamy and less potent bar.
As for added cacao butter there are many brands that use a lot of extra cacao butter and that are marketed as the most healthy choice. If you pay attention you can feel and taste the make up of the bar. Lastly I challenge you to taste and compare and see and feel which brand truly gives you the benefits and energy and mood boost. The way it makes you feel as you eat it, 5 and 10 mins after should tell you more than a thousand words about cacao percentage and the potency & effectiveness of the cacao properties. Trust your feeling after 2 squares.