I understand that it has a 50 year expiration date, though I believe this was an approximation on behalf of Wizards, even though this is an infernal contract (and would invalidate it). Thus, I believe the 1494 DR date is simply a mistake by the authors. BG3 comes after BG:DiA, as those tiefling refugees reference "the Descent" which had already happened.
Can you please give me a source for the 1374 DR date for BG:DA. Where does it say this? Is it in a sourcebook or the game itself?
Do you know what is truly invalid in the infernal contract? It's not the expiration date, buddy. Thavius being High Overseer of Elturel. Thavius surrendered the city in his "capacity as High Overseer of Elturel", yet signs it at a time when he was a priest of Torm, NOT the High Overseer, and in fact the vampire High Rider was still the legitimate ruler, meaning Thavius had no right or authority to surrender the city. That implies this part of the contract is actually invalid. Read the link.
https://forgottenrealms.fandom.com/wiki/Thavius_KreegBaldur's Gate Dark Alliance's time period was mentioned in the game itself, as I recall, I don't think there are no sourcebooks mentioning anything connected to BG:DA. 1374 DR is also known as the Year of Lightning Storms.