I am not sure if
@Chief position is that the Vai are not Mandingo or if he is saying that they are not Mande. Maybe he can clarify that for us, because the Vai are clearly a Mande people but he might be stating that they are not Mandingo.
My position is that all Mande people are Mandingo or Mandenka, because Mandeka is two words "Ka" which means "citizen of Manden" "people of Manden" or "Subjects of Manden." Of course the Arab or Fulani word for Manden is Mali (which is actually Mauritania). So Mandenka is "Mande"+"Nka." Mandingo/Mandengo means "Mande +Ngo", which is the same thing as Mandinka and Malinke.
@Chief has stated that Mande is distinct from Mandingo, Mandinka and Malinke, because Mandingo/Mandinka/Malinke are actual tribes within the larger Mande family. I concur with him that is how those groups are interpreted now, but research that I have reviewed showed that they are not distinct and the only difference between those specific tribes now and other Mande groups is that other Mande groups moved into different regions where they mixed with other local ethnic groups.
QI: some quite interesting facts about Mali
Saylor.org's Ancient Civilizations of the World/Empire of Mali - Wikibooks, open books for an open world
History of The Djembe
My maternal line is Mende from Sierra Leone. My paternal line is Bissa from Burkina Faso. Both of those are Mande groups, but on DNA tests my father shows up as Mandingo and my mother shows up as Mende/Mandingo. Mende literally means Mande.