private IEnumerable<DateTime> extractIncompleteWeeks(IEnumerable<DateTime> dates)
{
    var mondays = dates
        .Where((d, i) => d.DayOfWeek == DayOfWeek.Monday)
        .Select(d => d.Date);

    var results = new List<DateTime>();

    foreach (var monday in mondays)
    {
        var fullWeek = new HashSet<DateTime>(dates.SkipWhile(d => d < monday).Take(7).Select(d => d.Date));

        if (fullWeek.Last().Date == monday.AddDays(6).Date)
            results.AddRange(fullWeek);
    }

    return results;
}