def increment_index_versions(client, old_indices: list):
    """
    Increment versions numbers for new indices, these kind don't matter because they should always be aliased to
    the original format of {app_label}_{cls.__name__.lower()}_{year}.

    :param old_indices: indices to be updated
    :return: indices names that are going to be reindexed into.
    """
    new_indices = []
    for index in old_indices:
        index_name = list(client.indices.get(index).keys())[0]  # in case we've already aliased this index
        if '_v' in index_name and index_name[-1].isdigit():
            name, version_num = index_name.split('_v')
            new_index = f'{name}_v{int(version_num) + 1}'
        else:
            new_index = f'{index}_v2'
        new_indices.append(new_index)

    return new_indices