I'd like to premise that my knowledge of latin is limited to what I'm studying in high school. Now, as far as I know, Classical Latin was actually used by common people at the beginning, like, about the times when Rome was founded. Then it evolved into Vulgar Latin as everyday language got used and re-used by common people; but when a writer or poet had to write something, he used the rules of classical latin, as they were officially considered "the rules". It's like when a language, as it could be english, develops sayings and slang that are not considered properly part of the official language: in fact a university professor wouldn't use them in his writings; but as the time passes, everyday language continues changing, while "cultural" language remains quite back.
Fluent (on a good day): English, Spanish
Can understand: Latin, Toki Pona