As far as I know, Beamdog doesn't have a "box version", the Enhanced Edition itself doesn't have one (maybe on consoles?). I could be wrong, but I don't think is possible to even trade the original Icewind Dale box version for a GOG key. Anyone with a better understanding of french? (I used google...).

GOG Connect was a very very short-lived arrangement that allowed users to redeem sime retail versions of games on GOG. Maybe that's how you did it at the time. It's not feasible anymore, and there's no plan to bring back that possibility.

Il y avait eu, assez brièvement, le GOG Connect, un arrangement qui permettait de faire reconnaître sur GOG certains jeux anciennement achetés en version boîte. C'est peut-être comme ça que tu avais pu faire passer ce jeu sur GOG. Mais ce n'est plus du tout possible, ce système a été arrêté assez vite, et ils ne vont probablement jamais le remettre en place.

GOG Connect was for Steam.

GOG Reclaim was for a select few retail editions and Icewind Dale isn't among them. I looked at the Internet Archive page from 2015 and it doesn't seem like the list of eligible games has ever changed.
While the dedicated page is gone now, word from staff is that the CD keys for eligible games should still work, when entered into the Redeem Code page. But that's not relevant to this thread.

According to a thread on Steam, the boxed edition doesn't contain any redeemable code for an online store.

According to GG.deals, Icewind Dale was never on giveaway either. I see no way to have ever redeemed this game for free.

Je t'aime moi non plus comme ci comme ça. Non, je ne regrette rien.

Sinon, ce jeu est très souvent en promo. Par exemple maintenant, à 4,79€.