According to Baldur's Gate: Descent into Avernus, the Companion was summoned in 1444 DR, the Era of Upheaval.
That day came in 1444 DR, when Elturel was conquered by a vampire lord. A priest of Torm named *** appealed to any power to help him save his holy city. In that instant, *** emerged from a pillar of fire and offered him a deal, which *** readily accepted.
In the relevant contract, it said that Elturel was doomed after 50 years from then.
I further recognize that this dispensation will last fifty years, after which the Companion will return whence it came...
That means the Fall of Elturel actually took place in 1494 DR, the Year of Twelve Warnings.
However, the Baldur's Gate Gazetteer in the same module describes the city as of 1492 DR. Certain events described in the Gazetteer are supposed to coincide with the Fall of Elturel. For instance:
Ravengard was recently tricked into attending a diplomatic summit in Elturel, unaware that his political enemies in Baldur's Gate orchestrated this meeting in a fiendish plot to remove him from power. In his absence, the Flaming Fist is leaderless, the council rudderless.
This is mentioned in Chapter 1 when describing the Fall of Elturel.
A tenday ago, Grand Duke Ulder Ravengard left Baldur’s Gate with a company of Flaming Fist soldiers on a diplomatic mission to Elturel, accepting a formal invitation from Elturel’s High Overseer, Thavius Kreeg.
Interestingly, in the early-access version of the video game Baldur's Gate 3 made by Larian Studios and approved by WoTC, which is a sequel to Baldur's Gate: Descent into Avernus, the current year seems to be 1492 DR. To verify this, you could go north of the Risen Road to find a Tollhouse inhabited by some self-proclaimed Paladins of Tyr. In the basement, you will find a Tollhouse Ledger on the body of a dead Toll Collector, which states that the current year is 1492 DR.
Therefore, canonically, the event took place either in 1492 DR or 1494 DR, as far as I can tell. Has anyone settled this discrepancy? Which year is it?