Kanban in IT world in my experience implies approach where you focus on the work and tasks as they come based on priority. It doesn't imply what is on the board is finished strictly by some date, as the whole premise is that you can't really know.
SCRUM implies sprints where you agree in advance what will be actually pulled into sprints and delivered by the team so spillovers are not really expected / wanted.
I think that we are agreeing that Kanban and estimates aren't really analogous