When is Art Finished? A not so deep question

I passed a bank branch in my neighborhood this morning. The side wall was painted with what could only be described as a kind of abstract expressionist mural. When I went inside to tell the tellers that I thought it was really interesting, they told me it's not finished and that the finished mural will be a kind of tableau of different houses and buildings in the neighborhood.

So is an unfinished mural art if people see and respond to it as art? If it were a text, I can imagine the debate between Wolfgang Iser, Stanley Fish, and E.D. Hirsch, but I don't know enough about art criticism to imagine who the relevant art critics would be.