Alien
The "Director's Cut" of Alien isn't a true director's cut. Ridley Scott's preferred cut is still the 1979 theatrical cut. When Fox was getting ready to do the Quadrilogy box set, they wanted each movie to have two versions, so set about adding deleted scenes back into Alien. They asked Scott if he'd like to do a new cut, and he agreed - not because he thought it was a good idea, but because he didn't want Fox to fuck it up. So the "director's cut" of Alien is essentially a "what if?"-type alternate version. It's even a minute shorter than the theatrical cut, because Scott didn't just add stuff in, he trimmed scenes to make the movie move by a bit quicker for modern audiences.
Aliens
Aliens, on the other hand, is different. Fox thought that the cut James Cameron submitted to them was too long, and ordered that it be cut down to a specific length or shorter. Since Cameron couldn't really say no, he went ahead and did it. (I believe that when this happened, he wasn't done shooting the sentry gun scene yet, so that was one of the first scenes to go.) That's the theatrical version. The "Special Edition" of Aliens Cameron's preferred cut, essentially his Director's Cut.
Terminator 2
The story with Terminator 2 is basically the same as Aliens.
Alien³
Alien³, on the other hand, was fraught with problems from the beginning. There were many script rewrites before and during production, and David Fincher was a new director at the time, so Fox could pretty much make him do whatever they wanted him to do. As such, when time came to edit the movie, he got frustrated that he didn't get the footage he wanted. After trying for a while, and getting a mostly-finished workprint done, Fox said that it was too long, and he said "fuck it" and washed his hands of the whole mess.
Fast-forward to Fox working on the Quadrilogy set. They have the theatrical and alternate versions of Alien and Aliens, but only the theatrical cut of Alien³. They asked Fincher if he wanted to recut it, but he said he couldn't make his preferred version without starting from scratch and re-shooting it. So they took Fincher's last workprint and tried to essentially recreate it as best they could. Some scenes never had ADR (dubbing) done, so they used the on-set audio and subtitled the dialogue that was hard to hear. For the Blu-Ray set, they got Sigourney Weaver and Charles Dance to come in and ADR those scenes, so the audio is consistent throughout. They also had to add in some new CGI to finish effects scenes that were never finished.
So neither version of Alien³ is a director's cut. The "Assembly Cut" is the closest approximation, but it's not there. Personally, I think the "Assembly Cut" is vastly superior to the theatrical cut, but there are those who disagree (and those who don't give a shit because they hate Alien³, though I quite like it, at least the "Assembly Cut").
Alien: Resurrection
Alien: Resurrection's alternate version is just your standard studio-made "extended cut," where they just plopped some deleted scenes back in. I think they also recreated the original CGI opening shot of the movie, but I don't know for sure because I've only ever watched this abomination of a movie twice, and I've never seen the extended version. I have no idea which version the director prefers, or if he was involved in the creation of the extended version or not.
Blade Runner
And finally, Blade Runner. Erm...here we go.
Theatrical cut has bad Harrison Ford narration and a tacked-on happy ending, because the studio felt that audiences wouldn't understand the movie without the narration, and because they thought audiences wouldn't like such an ambiguous ending. Said tacked-on ending includes outtake helicopter shots from The Shining, and generally has a radically different feel from the rest of the film.
In the early '90s, someone accidentally screened the workprint version (no happy ending and no narration except for at Batty's death; the last reel or two had temp music, too) instead of the theatrical cut. People loved it, so that version started getting shown as the "Director's Cut" in theaters.
Seeing an opportunity, the studio asked Ridley Scott if he wanted to make a true director's cut. He basically said he was too busy at the time, but gave them some notes on what he'd like changed.
So, the 1992(?) "Director's Cut" of Blade Runner is the US theatrical cut, minus any narration, minus the happy ending, plus a poor-quality version of Deckard's unicorn dream/vision (more a dream in this version since Deckard appears to be sleeping).
Scott was less than satisfied with this version, since none of the editing was changed after the narration was taken out and the unicorn scene wasn't quite right.
So, in the 2000's, when they were getting ready to do the Blu-Ray, Scott had time, and offered to create his own true Director's Cut. The studio agreed, and "The Final Cut" was the result.
The Final Cut of Blade Runner features no narration; in the scenes that originally had narration, the editing is much closer to the workprint version, so there's not a bunch of pointless dead space; a few shots that were originally only in the workprint version (mainly outside the club where he finds Zhora); the properly-restored version of the unicorn vision (with Deckard being awake); no happy ending; re-done color timing throughout; and some continuity/effects fixes, such as the head of Zhora's stunt double going through the glass being replaced with the actual actress' head, the background behind Batty when you first see him replaced since it's a shot from later in the film (and Tyrell's hand on his shoulder is painted out), and - my personal favorite - the shot of the dove flying into the air at the end has been completely redone, because the original was clearly shot out in the parking lot when they realized they didn't have that shot - among other small changes like that (the wound on Deckard's cheek that appears before he gets it is erased in those shots, for instance).
So the Final Cut is Ridley Scott's true director's cut of Blade Runner, though the version billed as the "director's cut" is a close approximation.
Oh, and the International version of the theatrical cut had some particularly violent shots in it that were cut from the US theatrical version - these shots were not restored in the '92 director's cut, but were restored in the Final Cut.
So ... does that answer your questions? Msycamore's movie-censorship.com link is a good resource for stuff like this.