Chocolate "percentages" (for "pure" dark chocolate, anyway) work as pretty much as follows:
70% chocolate is 70% cocoa, 30% sugar, and (yes, more than 100% total) a percentage of cacao butter, at least if it's the real thing.
For the real thing, the fat ratio is fairly consistent, though it may vary slightly with the raw ingredients. Two examples from a chocholic's stash.
Both are listing cacao solids / sugar / fat percentage, where cacao solids and sugar add to 100% for "chocolate percentage", and the fat relation to cacao solids is 53-54% for those examples (40/75 and 38/70)
So, assuming the cacao butter has not largely been siphoned off to the cosmetics industry, the weight of your 99% chocolate is actually 152-153% of the weight of the cacao solids in it. Further math says the cacao solids are about 65% of the combined cacao solids and cocoa butter mass, pretty much.
So if you have 100 grams of 99% chocolate, it's got 64-65 grams of cacao solids, and 26-27 grams of sugar added to that would make 126-7 grams of 70% chocolate.
It's mostly confusing because of the special way the chocolate industry uses "percentage" which is not intuitive.