foreach (var car in allCars)
    {
        int firstCheck = DateTime.Compare(currentDate, car.TechnicalInspectionDate);
        int secondCheck = (car.TechnicalInspectionDate - currentDate).TotalDays;
        if (DateTime.Compare(currentDate, car.TechnicalInspectionDate) >= 0 || (car.TechnicalInspectionDate - currentDate).TotalDays <= 30)
        {
            result.Add(car);
        }
    }