C# DateTime AddMonths 的错误用法导致跳过日期

    class Program
    {
        static void Main(string[] args)
        {
            DateTime now = DateTime.Now;
            for (int i = 0; i < 60; ++i)
            {
                DateTime dt2 = now.AddMonths(+i);
                //Console.WriteLine(dt2.ToString("yyyyMM"));
                DateTime dt3 = now.AddDays(+i);
                Console.WriteLine(dt3.ToString("yyyyMMdd"));
            }

            Console.Read();
        }

        // AddMonths的错误用法
        private void error()
        {
            DateTime now = DateTime.Now;
            for (int i = 0; i < 20; ++i)
            {
                // 这种在2020-12-31执行时会退跳过202102
                now = now.AddMonths(+i);
                Console.WriteLine(now.ToString("yyyyMM"));
            }

            Console.Read();
        }
    }