That I've seen, the problem is worse than that. A movie merely says it's "based on a true story". If you're a lawyer or literature professor, that "based on" might be correct usage - since 40-ish percent of what the movie told was true. The other 60-ish percent was utter fiction.
Meanwhile, people who saw the movie and found it decently engaging are busy convincing themselves that it was 99% true. And 99% of 'em will never bother to check.
I coulda added another "That I've seen" disclaimer to my second para. My dataset is just friends & family who I've seen "based on a true story" movies with, where I happened to know the history.
The term to describe my "99%" isn't "dumb". It's "don't care".
It's all variations of Gell-Mann Amnesia. Any portrayal is a betrayal.
Of course, if I'm going to talk about something I know deeply, I'm almost certainly going to begin with "this is all incorrect in the details, but correct in general" or similar.
For those sufficiently pedantic, true. OTOH, there's a rather wide spectrum in how well (say) Mitchell's Gone With the Wind, Ken Burns's The Civil War, and McPherson's Battle Cry of Freedom portray the U.S. Civil War.
Meanwhile, people who saw the movie and found it decently engaging are busy convincing themselves that it was 99% true. And 99% of 'em will never bother to check.