The simple answer is no. Mound building was a very widely practiced act in North America, and Middle Mississippian culture was a blend of lots of concepts and elements from much of the Southeast. If we look at Cahokia's influence it is even fuzzier, we see them impacting communities in all directions. Even at Cahokia itself we see elements being brought in from all over North America, it was a city of people from many cultures. In fact we really have no idea what language was even spoken at Cahokia, a few language families are seen as candidates but again the number of cultures involved make it hard to pick out one as the clear example.

So not only was Cahokia a true melting pot of cultures, but it also was one that was essentially abandoned. People simply packed up and left over time, bringing back elements of Mississippian culture with them. It is not so much that we have no idea who the direct link is to Cahokia but instead that we have a lot of elements brought to many cultures. Within 250 years we have European accounts from people like De Soto who describe cultures in the Southeast that have elements quite similar to what we see at Cahokia, elements that made Cahokia unique from an archaeological perspective. But as with other elements, we see a wide range of communities met who practiced remnants of Mississippian culture.

I think a great comparison would be Rome and the impact Rome had on Europe. The Romans left their mark directly and for generations those impacts became parts of the local culture. Roman culture became something beyond a genetic lineage, one could argue most of Western Europe was a descendant of Roman culture. Middle Mississippian culture may have had a similar impact, it became so far reaching and imbedded in the communities of Eastern North America that people were acting Middle Mississippian without actually fully understanding who they were emulating.

Tldr: Middle Mississippian culture became unattached from any genetically linked group, to find any direct lineage is next to impossible. There is no account because the culture became imbedded everywhere, and odds are that within a few generations it became so common that no one gave a second thought to who they may have been emulating.