Повторяющиеся значения при фильтрации "многие ко многим" + "многие к одному"

class Section(models.Model):
    title = models.CharField('Заголовок раздела', max_length=200)
    text = models.TextField('Текст раздела', default="Текст")
 
class Reference(models.Model):
    title = models.CharField('Материалы', max_length=200)
 
class Subsection(models.Model):
    section = models.ForeignKey(Section, on_delete=models.CASCADE)
    reference = models.ManyToManyField(Reference)
    title = models.CharField('Заголовок подраздела', max_length=200)
    text = models.TextField('Текст подраздела', default="Текст")

def section_page(request, section_id):
    object_section = get_object_or_404(Section, id=section_id)
    references_list = Reference.objects.filter(subsection__section=object_section).order_by('title')
    
    context = {
        'object_section': object_section,
        'references_list': references_list,
    }
 
    return render(request, 'section_page.html', context)

def section_page(request, section_id):
    object_section = get_object_or_404(Section, id=section_id)
    subsection_list = object_section.subsection_set.order_by('-date')
    references_list = []
 
    for s in subsection_list:
        references_list_i = s.references.all()
        
        if len(references_list_i) != 0:
            
            for n in references_list_i:
                
                if n not in references_list:
                    references_list.append(n)
        
    references_list.sort(key=lambda references: references.design)
    
    context = {
        'object_section': object_section,
        'references_list': references_list,
    }
 
    return render(request, 'section_page.html', context)