now the link
Gensokyo Timeline, and user talk
Use the "Talk" page of a user for "messaging" on the wiki, usually when someone want to discuss something, they create a topic on the User talk page and both choose one page that will be used for the discussion (or just go back and forth between both user talk page). You're free to manage your user page/talk page however you want, but it would be better if you wouldn't remove the message history while the discussion is still ongoing at the very least. Just an example I guess, look there : User_talk:Mami.
Now going back to the point. I wasn't "agitated", I just created that discussion to explain why I cancelled the changes, and why your changes made no sense in the context of that timeline. If you felt "aggressed" then I'm sorry, but I prefer explaining stuffs when I make some changes of this kind rather than just undoing and hoping that the person understood why I did it from the few words in the change history.
As for your question, the answer is right in the article introduction:
There are two calendars in common use in Gensokyo: the Gregorian calendar, which is the main calendar used by Gensokyo's inhabitants, and a youkai lunisolar calendar, which is generally restricted to Youkai Mountain. The youkai calendar is based on the phase of the moon - as a result, it runs somewhat offset from ours. All events in this timeline will use the Gregorian calendar with estimated youkai calendar dates in brackets for important events where they can be deduced (under the assumption that the youkai calendar is determined in the same way as the Japanese lunisolar calendar), except for articles from the Bunbunmaru Newspaper and the Kakashi Spirit News, which are originally dated in the youkai calendar (the numbering is assumed to represent issue numbers in each month; see Notes below for more details). CE (Common Era) and BCE (Before Common Era) are used instead of AD and BC.
(and I also invite you to read the first section Gensokyo_Timeline#Month_names where the numbering system of the months used in the article in the youkai luni-solar calendar is described)
Most of the people in Gensokyo use the Gregorian Calendar, so Reimu & cie will mostly celebrate New Year at the same time than the people of the Outside World.
But New Year in the Youkai Luni-Solar system does not take place at the same time. You know, just like in the real world the "chinese New Year" is not celebrated on January 1st as it is based on the chinese lunisolar calendar.
The reason this article is using the Youkai Luni-Solar Calendar is (imo, since I wasn't around when they started making this article, but based on what we can read on the Gensokyo Timeline Talk Page) that is was started of as a translation of the jp thwiki article and that's how they did it I guess, and that most dated articles are from the Bunbunmaru Newspaper and the Kakashi Thought Report which are dated using the Youkai Luni-solar system (since the articles are written by the Tengu).
But the main problem with your changes (because I will agree that this system can make thing confusing) is that it was not consistent with the rest of the article. You basically changed the date of the beginning of PCB to be after the end of the incident.
Gotcha. That's damnably confusing.