So I've noticed something. The dates on the wiki 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
(at the top next to the words Matrix Blaster and 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
So, with those three assumptions out of the way, we can start to do calculations.
I used the Tron Cycle conversion chart from 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, by subtracting 1 TC from the date (According to the TRON: Evolution TRON files, they start at 1, not zero) and converting 300 TCs into days, then working the days backwards, accounting for the leap years 1984 and 1988.
November 5th, 1983 is the start date for the Grid.
From the same date for the Coup, we can figure out when Legacy happened, using the screensaver running on Flynn's terminal. The time given is 20 years, 11 months, 20 days, 16 hours, 22 minutes, 16 seconds, and some other random time that according to IMDB, updates 15 times per second. 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.
Thus, The Grid was created November 5th, 1983, the Coup happened and Flynn disappeared November 3rd, 1989, and TRON: Legacy happened October 25th, 2010.