You can find the nutrient content of raw and boiled cassava leaves in the Food and Agriculture Organization West African Food Composition Table - section 04: Vegetables and their products. This resource was updated in 2012 and is available as a PDF or as a database. The PDF provides an explanation of the abbreviations and analytical techniques in addition to the data. The values are not identical with the ones you shared, but it would probably be better to use the updated FAO database values. The procedures for analyzing nutrients in foods are improved over time and additional samples may have been added to the database.
The resource mentioned by Kay is a very good one to find the information you are looking for (pages 13-15). You can find other Food Composition resources (http://edn.link/foodcompositiontables) in our Key Nutrition Resources Collection (http://edn.link/keynutrition).
Thank you for bringing your question to the ECHO Community, and thanks to Kay too for her response!