So I've noticed something. The dates here are horribly inconsistent. One page will give one date, another gives a different date for the same event.
So I went and I decided to try to figure out exactly WHEN the filmmakers set different defining events. Mainly, I just wanted to know my birthday in Tron Cycles. :P
So here's how I figured things. There are three assumptions needed. Assumption 1: The date shown at the beginning of every TRON: Uprising episode (when it says "Accessing Archive Data, at the top next to the words Matrix Blaster and I think Vice Squad, maybe Space Paranoids) is the last date that Flynn rezzed into the Grid.
Assumption 2: An entire cycle had yet to pass between the creation of Anon and the Coup.
Assumption 3: The time screensaver seen in Legacy is accurate.
So, with those three assumptions out of the way, we can start to do calculations.
I used the Tron Cycle conversion chart from here on the wiki.
Using TC 301 (Anon's creation date) as the date of the Coup in Tron Cycles, and November 3rd, 1989 as the final rez date of Flynn (The date from the Tron: UPrising opener), we get a start date for the Grid.
November 5th, 1983.
From the same date for the Coup, we can figure out when Legacy happened, using the screensaver running on Flynn's terminal. That came out to October 25, 2010.
I could not find any official evidence that Sam's pranks on ENCOM corresponded every year to the anniversary of Flynn's disappearance, what I believe is more likely is that he pulled something at big events, like the Space Paranoids Online and Encom OS12 releases.