Most of the following production documents were originally owned by Michael Milgrom, the property master for the Los Angeles reshoots on ALIEN³. They provide a detailed overview of the scenes that were still left unfinished only a few months before release—as well as the substitution of the dog, Spike, as the alien’s host on Fury 161, instead of the Ox, Babe, as was originally scripted and shot.
Confusingly, it seems multiple versions of the script were still at play even at this very late stage. The screenplay draft seemingly used by Milgrom for March reshoots was dated September 4, 1991; the substitution of the dog for the ox is still not reflected in this draft. The original opening with the queen chestburster escaping from the drowning Newt and entering Ripley in the EEV is likewise retained. In late April 2019, samples of a previously unseen draft with a later date of December 17, 1991 surfaced online. This draft contains a radically different alternate opening sequence where a chestburster erupts from Hicks, and a facehugger somehow simultaneously attaches itself to Ripley.
This version of the opening seems to have been abandoned just as quickly as it had been hastily rewritten (note the Wayland-Yutani typo). With both versions of these crucial establishing scenes still left unfilmed by the time reshoots began in Los Angeles, it appears the infamous egg on the Sulaco was introduced as a last minute alternative. It should be noted there is still no mention of any eggs in all available versions of the script—even, it seems, in the final drafts used for the reshoots; at most, only a facehugger and a chestburster are described as being aboard the Sulaco, still a more plausibly ambiguous scenario than the egg(s). The facehugger itself would be realized onscreen in the original cut of the film as the “Super Facehugger”, capable of implanting multiple embryos, including a queen.
Adding to the chaos of this hastily assembled opening sequence, the Super Facehugger was also abandoned for the reshoots, replaced with a standard facehugger design as seen in the prior two films—which begs the question of how this normal facehugger seemingly implanted two embryos, one in Ripley and the other in the dog, Spike. Explaining this away seems to have been the purpose of the alternate opening with the chestburster coming out of Hicks (presumably somehow birthing the four-legged Runner?), and a facehugger impregnating Ripley with the queen. With that scenario abandoned along with the earlier Newt impregnation, the reshoot call sheets and prop lists seem to have an (extremely improbable) explanation for the multiple aliens: there was going to be two eggs on the Sulaco, implying more than one facehugger. For whatever reason, only one of these eggs made it to the screen.
All these reshoots create a glaring continuity error in the far superior Assembly Cut/Special Edition version of the film, as featured on the 2003 Alien Quadrilogy and 2010 Alien Anthology home video releases—because the Super Facehugger was not used in the reshoots, it does not appear in the opening of the Assembly Cut either, making for a somewhat jarring discrepancy between the two designs, both ostensibly intended to be the same creature.
The Assembly Cut also retains the brief shot revealing the egg, which strictly speaking should not appear, since it is part of the same reshoots that included the dog subplot and the revised chestburster ending. Despite these troublesome onscreen mismatches, it should be noted that the other films have their own fair share of continuity errors (see most glaringly: the shot of the alien’s tail snaking up between Brett’s legs being repurposed for Lambert’s death in ALIEN).