I had a bit of a left-field thought today. Have they intentionally screwed with the calendars to promote the idea of climate change, global politics, and to disconnect people from the sky, stars, and their natural environment.
I propose that the length of the true year is between 360-364 days in length. I think 364 is the most likely.
364 / 28 = 13
There are 28 days to the moons cycle, and this would break nicely into 13 lunar months. I think we are supposed to use the moon to tell dates and time alongside the stars, not the sun.
The sun is being used to throw everything off. It's part of their solar worshipping. They changed the calendar to be solar and adjusted to make it fit, but the sun was never supposed to be used for time keeping.
It is causing an extra 1.25 days every year to shift the actual seasons around. Very subtle, and not really enough to notice except over a lifetime - which would only be corroborated with at least 60+ years to truly notice as your idea of the months would be respective of your birth year.
This was likely done around the 1700's and would have coincided likely with the American/french revolution (revolve) and it pushed the ideas to the forefront of society.
Since this would result in approximately 100 years seasonal shifting, you could setup narratives for climate change (cooling and heating) because they are being told that December is supposed to be a certain way when in fact it's supposed to be tracked with 13 lunar months instead.
I think about this often. I've lived in the same area for over 20 years now. It's anecdotal, but I remember that when I first moved here, snow was guaranteed to fall a couple weeks before Halloween. And winter would be pretty much over by April. The last few years, snow has come at earliest on Halloween, but usually closer to Thanksgiving and then sticks around until nearly June. Again, anecdotal, but I have definitely noticed it.