code: def add_version_iri(graph, epoch):
      
      for ont in graph.subjects(rdf.type, owl.Ontology):
          for versionIRI in graph.objects(ont, owl.versionIRI):
              graph.remove((ont, owl.versionIRI, versionIRI))
          t = ont, owl.versionIRI, make_version_iri_from_iri(ont, epoch)
          graph.add(t)
docs: Also remove the previous versionIRI if there was one.