By "dexenoethnic exonym" (my own coinage for the purpose of this particular question) I mean an ethnonym/glottonym derived from a name originally applied to a (language of a) different ethnic group, especially (though not necessarily exclusively) linguistically unrelated. Oft-cited examples may include the Bohemians, Macedonians or Wends, to name just a few. A similar case might be the Indians.
It appears a common development is this:
Group A ethnonym → Group A toponym → Group B ethnonym
In other words, an area gets its name from a group that inhabits it, then another group "inherits" the same area, which later serves as a basis for the name of its new inhabitants, perhaps an exonym at first.
I wonder whether there is a study focusing specifically on this area of onomastics. One of the reasons why I would like to learn more is the frequent (ab)use of toponymy and ethnonymy in nationalist propaganda of all sorts (e.g. claims such as "Our nation is superior, because our nation is oldest, because the name XYZ is attested as far as N centuries back!" etc.).
Intuitively, I feel developments like this are fairly common and result from language contact situations, but having a comprehensive list of documented cases from all over the world, preferably categorized or typologized, would be immensely helpful. I will be grateful for any useful references, but concrete examples are also welcome, and so are any comments or suggestions. Many thanks in advance!
EDIT: If there are no studies dealing with this area specifically, I would be happy to pursue the topic myslef, in which case, however, it would be good to have an appropriate term. I am not sure "dexenoethnic exonym" is very fortunate, so terminological suggestions will be appreciated as well.