The new version of the nutrition label specifically calls out added sugars [1], so it sounds like if there are gray areas the FDA has been able to decide on a standard.
Right, but right now there's not a super strong incentive for companies to try and manipulate their added sugar label. It can be a marketing thing for some brands but if added sugar was actively penalized then you would start seeing better attempts to keep foods sweet with "non-sugar" sources.
[1] https://healthcare.utah.edu/healthfeed/postings/2018/05/nutr...