Nothing is IMPOSSIBLE.
And the mural is just a goof that comes along with telling sequels over long distances of time. Things change in the creative process that can't be foreseen. Nothing is set in stone. Characters get recast (The Hulk in Marvel), imaginary worlds undergo drastic revisions (Alfonso Cuaron basically rebuild everything about Harry Potter when he took over & nerdrage was nigh) & stories evolve. It would be hypocritical to attack Scott's two prequels for a mural seen in one shot when Rebuild (I really have to write an essay about how similar these two new-sagas INCLUDING how little they care about superfluous side characters & super strict continuity, things both are routinely attached for) spends two movies actively building up Eva Mark 6 as this ALL-IMPORTANT thing & then just throws it aside almost entirely. Not necessarily because Anno was pulling a bait & switch but because he realized the story he wanted to tell didn't need Mark 6, The vision the filmmakers had evolved from one film to the next because the films in both franchises are not being made by a committee of TV minded producers who are trained in episodic stories. They're being made by artists who have their own weird/wonderful interests & fetishes. You either roll with the punches & go with the story or you nitpick about how thing X in this film doesn't correspond to something that occurs three films down the line. Like how unimaginative Aliens bros are saying Scott has erased the Queen Alien which is nonsense, a key part in the creation of life would be giving said life the option to procreate, hence David creates a Queen at some point... or after settling on Origae-6 things get out of David's control - continuing the circle these films have shown where the life you create destroys you, the Engineers are killed by their biological weapons/humans, humans are killed by the AI they create & the AI is destroyed by the PERFECT ORGANISM (to quote another AI in the original Alien, makes sense a robot would love something created by a robot).
I think Scott was telling the film he was focused on that moment. When/if it comes time to tie things into the original Alien it wouldn't take much to do so.