I've known about this calendar for years; but with this approaching Pesach, I decided to look at it a little more closely.
I'm still proving out much of the evidence that I have begun to gather; but I've tentatively already changed my Pesach plans.
Here is one piece of evidence that didn't take much research:
Jubilees 6
36 For there will be those who will assuredly make observations of the moon
-how it disturbs the seasons and comes in from year to year ten days too soon.
Lunar cycle = 29.5 days
29.5 X 12 = 354
364 - 354 = 10
37 For this reason the years will come upon them when they will disturb (the
order), and make an abominable (day) the day of testimony, and an unclean day
a feast day, and they will confound all the days, the kodesh with the unclean,
and the unclean day with the kodesh; for they will go wrong as to the months
and Shabbats and feasts and jubilees.
38 For this reason I command and testify to you that you may testify to them;
for after your death your children will disturb them, so that they will not make
the year three hundred and sixty-four days only, and for this reason they will go
wrong as to the new months and seasons and Shabbats and festivals, and they
will eat all kinds of blood with all kinds of flesh.
It's put in more symbolic terms in the Torah, for example, Maryam, (a.k.a. Miriam), stands against Mosheh, (in one of the passages referenced in my previous post, BaMidbar 12), and what happens? She becomes leprous, white as snow all over, white like
the moon because she stood against
the sun, (Mosheh's face not only shone with glory, as we read, but even shone as the sun in the properly understood symbolism: see also Matthew 13:43).
Maryam is then put out of the camp for how long? that was for seven days, and bnei Yisrael journeyed not while she was put out of the camp.
The other four days, which are added into every year to make the year 364 days, end up being actually codified in the story of Yiphtah, to commemorate the daughter of Yiphtah, a statute for Yisrael, and that passage refers the reader back to Devarim1&2.
The whole eleven days are revealed in the spies having gone to spy out the land: for in that passage the Most High says that bnei Yisrael had provoked or tempted Him "these ten times", and yet, they proceed to do it one more time right there in the same passage by going up into the hill after it was already too late and judgment was decreed, (BaMidbar 14).
This was the first year of the Exodus, which therefore was a leap year: eleven days from Horeb the way of mount Seir as far as Kadesh-Barnea. Mosheh puts these eleven days all together between the tenth month and the eleventh month, (Devarim 1:1-3).