from typing import List


def check_sequential(
        reference: List[str],
        update: List[str]
) -> bool:
    """Helper to check if update continues sequence.

    Helps to check if updated dates are all in sequence.

    Args:
        reference (List[str]): Reference list of dates to be updated.
        update (List[str]): New dates to update.

    Returns:
        bool: True if sequential, False if not.

    """

    index = [i for i, item in enumerate(reference) if item in set(update)]
    index_it = iter(index)
    first_item = next(index_it)
    is_sequential = all(a == b for a, b in enumerate(index_it, first_item + 1))

    return is_sequential