Google rewrites history when you search for the 1984 film cast

This isn't uncommon in Google results. The other day I wanted to double check that Steve Carell was Gru in Despicable Me because I'm awful at remembering celebrity names. The search "despicable me cast" got a list where he didn't show up until you scrolled way down, past someone else (who appears to be a dubbed version's lead) credited for the role. I'm guessing the issue is really in whatever dataset they source movie casts from.

Is John Hurt controversial in some way that's not obvious from looking over his Wikipedia page for a minute that he'd be intentionally omitted?

I think this is because Google compiles these cast lists based on search proximity prevalence. So if you look up some actor and a movie in the same query many times it starts to assume the actor is in that movie. Maybe they combine this with some base scraping but I think it's highly unlikely they use some API or hand craft the lists.