Attempting to create multiple FactoryBoy objects only seems to create a single object

I'm attempting to write unit tests for an article system so I want several articles published on different dates to test that the correct number of articles are displayed. The trouble is it seems like only 1 object is created despite me calling the factory 3 times.

factories/article.py;

class PublishedArticleFactory(DjangoModelFactory):
    """
    Initial published article factory.
    """
    title = u'Test Article'
    tags = u'tag1, tag2'
    content = u'This is an article and I\'m not at all imaginative.'
    author = factory.SubFactory(StandardUserFactory)
    published = True
    published_timestamp = str_now()
    edited_timestamp = None
    slug = factory.lazy_attribute(lambda a: slugify(a.title))

    class Meta:
        model = 'articles.Article'
        django_get_or_create = ('slug', )

tests/test_views.py

class TestArticlesViews(TestCase):
    def setUp(self):
        # Every test needs a client.
        self.client = Client()
        self.article1 = PublishedArticleFactory.create(
            published_timestamp=str(
                datetime.datetime.strptime('10/01/2015', '%d/%m/%Y')
            )
        )
        self.article2 = PublishedArticleFactory.create(
            published_timestamp=str(
                datetime.datetime.strptime('15/01/2015', '%d/%m/%Y')
            )
        )
        self.article3 = PublishedArticleFactory.create(
            published_timestamp=str(
                datetime.datetime.strptime('01/03/2015', '%d/%m/%Y')
            )
        )

    def test_calendar(self):
        # Issue a GET request.
        response = self.client.get('/articles/2015/')
        # Check that the response is 200 OK.
        self.assertEqual(response.status_code, 200)

        print '\ncontext: ', response.context['object_list'], '\n'
        print '\narticle: ', self.article1.published_timestamp, '\n'
        print '\narticle: ', self.article2.published_timestamp, '\n'
        print '\narticle: ', self.article3.published_timestamp, '\n'

This test should render all articles published in 2015, but instead I just get a single object;

context:  [<Article: Article object>] 
article:  2015-01-10 00:00:00 
article:  2015-01-10 00:00:00+00:00 
article:  2015-01-10 00:00:00+00:00

It seems that article2 and article3 aren't created as separate objects, where am I going wrong?