Nah your reading too much into the "ooze" description, i think. It's very similar to the Carlos Huante design... except it's boneless, actually has a tail and the dome is transparent and "dolphin like". Huante inspired himself in the Belluga whale for his last design before he left, he probably started off from this description. His design has the "pair of bony jaws" in a few of his concept pieces. the chestburster stage does have the hability to "squeeze" itself into tight spaces like an octopus though. That hability isnt shown in the adult version.
The original Giger Alien shows up on the script. and is the one that Watts (Shaw) gives "birth" to.
The differences between these aliens are explained by David. There are many different compartiments with different eggs on the juggernaut, and each have been "tinkered with" differently. Holloway and Watts each "get" different facehuggers. There's no clear "protoxeno" here. No "evolution" into the Alien. The black ooze can mutate animals but doesnt give them the hability to give birth to "facehuggers" who then mate to produce the alien. There's none of that "Lindelofian" overcomplication in here.
One idea though. Spaihts script has a "hatchery" with many different eggs. Lindelof's version has the "Head" room with many canisters of varying size. Maybe their contents really are different. And fifield did get something different than Holloway. Someone has to get Lindelof at gunpoint to explain that mess. He'd probably just say "i dont know.. and isnt that cool? And mysterious?" Gah!