I don't know if this still applies, but sub-titles used to have only to contain a certain number of words or letters, so that they could be read swiftly.
And for some odd reason the people writing sub-titles were not issued with a manuscript, so unfamiliar names or concepts could quite easily be misunderstood - especially if the writer was unfamiliar with the speaker's dialect.
Next problem leading to mistakes was that it was piece-work and badly paid, so the faster you worked the more you earned.
And another unacountable idea was that programmes were submitted to the text writers very late, which was understandable enough with the News, but less so with a series, or Heaven forbid a play by Shakespeare, or a Restoration playwright.