Yes. L.R. Palmer's The Latin Language cites a document called the Appendix Probi, containing "notes on current errors of speech [which] were probably drawn up in the third or fourth century A.D." Some of the errors described in the book actually give us an idea of what vulgar Latin looked and sounded like. For example, Vulgar Latin apparently exhibited syncope, as in speclum, veclus, and tabla for speculum, vetulus, and tabula respectively.