Ravenloft is a part of Planescape but it has it's own exclusive setting as well.
1) Ravenloft was from before Planescape, as both the stand alone Count Strahd adventures, and as a campaign setting.
2) EVERY D&D setting from the 2nd edition era is technically part of Planescape. Just like every setting was technically part of Spelljammer too.
As the title says. Al Qadim is part of the Forgotten Realms setting. It takes place in Zakhara, which is to the south\south east on the Forgotten Realms map.
Yes the setting is in FR but it was always branded as it's own setting.
Exactly this. The Al-Qadim boxed set did not have the Forgotten Realms logo on it. The three other separate FR settings (Maztica, The Horde, and Kara-Tur/Oriental Adventures) DID get the logo, because they were supposed to be played as part of FR, while Al-Qadim was supposed to be either separate, or, if you had the FR boxed set, you could use it as part of the campaign setting.
So yeah, Al-Qadim should be treated as a separate setting.