The original series had no direct references to the Gregorian calendar.
The Second Formic Wars book The Swarm have the date of 2118AD for the events of that book (quoted in a note in chapter 2) which take place approximately 92 years before the start of the novel Ender's Game (or 97 years before the destruction of the Formic home world). That would place the destruction of the Formic homeworld around 2223AD.
But Shadows in flight has Bean's ship leaving Earth in 2210AD,
**Opening Line: **
The starship Herodotus left Earth in 2210 with four passengers
This is supposedly 8 years after the last battle which would put the destruction of the Formic home world at 2202AD. Those two dates are the only ones I can find and they don't match up. So the best we can guess is Ender's Game takes place somewhere between 2200 and 2225AD.
The books The Hive Queen and The Hegemon are supposedly published 41 years after the last battle in Ender's Game, and the Starways Congress founding happens somewhere after that.
From Speaker for the Dead, the colonisation of Lusitania is in 1886SC and Ender/Andrew arrives on Lusitania 1970SC, supposedly around 3002 years after the ending of Ender's Game, which would be either around 5204 or 5225AD depending on which of the aforementioned references you use, which would place the SC year 0 as either 3234 or 3255AD.
That's as close as I can guess it.
The SC dating in the books end up giving conflicting info too, because the founding is moved from around 60 years after the battle to something like 600 years after.
So anyway, given the 21 year discrepancy, which really isn't much given the 3000+ year time span, you can use the arrival at Lusitania to calculate other stuff in the timeline.
That whole attempt above at finding the answers is actually obsolete. The people at the Enderverse Wiki did a much more thorough job of setting up a timeline.
You can check it out here: https://enderverse.fandom.com/wiki/Enderverse_Timeline
I will put a quick timeline based on their calcs in a new answer