Baldur's Gate wiki has this to say:
The novels were set as the official version of the events described in the franchise in regard to the overall canon of the Forgotten Realms setting. Wizards of the Coast have however slowly started retconning this in the recent years. Now the canon is a mix of both the events in-game (including the Enhanced Editions) and the novels, though a lot of details are left ambiguous. Abdel Adrian is still the official version of Gorion's Ward.
I wish it would go into more detail about exactly which bits have been retconned, which parts are canon from the books and which parts from the games. I definitely know that the Abdel Adrian thing is canon, because he's in Murder in Baldur's Gate.
