I had an "oops" moment with a dark chocolate bar as well. There was an import brand of extra dark Belgian chocolate that I used to buy when it was on sale. It didn't give a % cacao, but the net carbs were the best I'd seen. Then one day I decided to plug the nutrition facts for that chocolate into MY PLAN. It wouldn't take it. I did the math and realized my mistake. The carbs number on the nutrition label had already accounted for the 6g of fiber per serving. It didn't say net carbs, but that is what it was. When I added 6g of fiber to the listed carb count the math worked.

Like your mishap, this too was very good chocolate. I suspected that there was something too good to be true about it. Yep - it was too good to be true. Sugar does that. I don't buy that chocolate anymore. I'd read that other countries often remove fiber from the carb count on their nutrition labels. I didn't realize that they could import it into the US labeled that way. Very confusing to the consumer.