I have come to the conclusion, that the overrides() method does not
match all of my requirements (especially the problem with overriding
across multiple projects). So I found another way to check if a method
implements an abstract method declaration.
I compare the signatures and check the type regarding the hierarchy and
their abstract flags and so on. Most of this data is present anyway in
my code, so it is less effort than determining all possibly needed
binding keys.
But I thank you for your efforts so far. At least now I understand the
mechanisms a little bit better.