But there's nothing established about the SJ in Alien. Nothing at all. It's hard to retcon something which has no firm basis to begin with.
The film estabilished that it was an alien lifeform. Dialogue. Had the film wanted to say it was a suit, it would have -- there are countless
ways to do that, visually or via dialogue. It wanted to estabilish that the thing was an alien, and it did.
Add to the fact that Dallas doesn't have the proper training to really say anything definitive about the specimen, there's nothing really contradictory. Aesthetic differences, yes, but there's aesthetic differences between a suit of armour from the 11th century to a suit of armour now. It's just how the designs and technology of the race change over the ages.
A retcon is something that alters a previously estabilished fact without breaking continuity. It's not a contradiction; it's an alteration
. It's different; the latter is confined in continuity.
It's kind of smoother going if I make a practical example. Let's say I make a new Alien
film, and decide to make Jones the cat a synthetic
cat. Does it break continuity? No, because there is not anything against this concept actually featured in the film. Is it a retcon? Absolutely! Nothing
had set up to it, nothing
implied or even suggested it. Jones was of course estabilished as a simple pet cat in Alien
, but my new film would retcon
him into a synthetic cat.