The current version of the calendar I have posted is version 7, and I believe Shiloh hasn’t been listed on the 22nd since version 4 of my calendar. Even if I placed the rare quests on the calendar every 9 days based on the average you are getting, it still would have been two days off. I do update calendars in this post as soon as I am able to correct any date discrepancies.
While I appreciate you doing the math, I fail to see what more you expect from me.
There is a comment at the bottom of the calendar that states rare quests occur every 7 to 11 days, and it is noted in the original post.