I will confirm this.. From chapters 1-7 in the light world i collected all bandages, did all warp zones and completed it A+. For the dark world i did the exact same thing except.. it gave me the 100% achievement after completing 7-18x so i was like "oh cool... let me look at my stats for the game" it showed Total progress 100%
Light World 100%
Dark World 98%
i guess the total progress goes over 100% giving you the achievement.