see
Pedantic Grognard
Indeed, to quote the first in-print publication of the gods of the Realms (back when the Realms were just one guy's home campaign that he used for examples in his Dragon Magazine articles), in the Dragon #54 (October 1981) article "Down-to-Earth Divinity":
And no, Maglubiyet was not made a servant of Bane then, or at any point until the Realms were entirely butchered. Nor was Grummsh identified with Talos, or so on.To adhere to the AD&D structure, however, requires a DM adopt, more or less wholesale, the “Nonhumans’ Deities” section of the DDG and Thrym and Surtur (the giants’ gods) from the Norse mythos.