I didn't include it, because the original question was where vi and its predecessors came from, not what offspring did it have itself.
Is the source history of these editors saved in the UNIX history GitHub project[1]? Is there significant code overlap or is your diagram more along the lines of inspired-by relationships?
There is not a lot of code overlap in most cases, even between ed and ex. The relationships are generally more about command sets than direct forking of code.