No, this is done because 13 4-week periods "loses" one day a year. So every 7 years, Nielsen has to add a week to Holiday to normalize things again. In 2021, the survey periods will come closer to matching the calendar months.
What they do not want is days from a prior year being carried into the next year. It causes some significant internal issues. Since the Holiday book is hardly used at all for sales except for the maybe 45 or so all Christmas stations in those markets, it is the "adjustment period" for each year. And, of course, the panel decays badly in those weeks, sometimes well over 10% falling off.