Well, the sad fact is the protestant revolutionaries were notorious for falsifying Scripture so as to mask their ideology. If they didn't change scripture, they would easily be identified as Satan's Mini-me's.
In the case of Luke 1:34, the mistranslation is very subtle. KJV translates it correctly. To a casual reader, there is no difference between "I know not man" and "I am a virgin"; but the implications are completely different.