Not true about Hebrew and civil dates matching every 19 years.
If you would look on a good calendar, at what time the Molad was 19 years apart, it would be a much closer match.
Despite the timing of the Molad, the actual day of Rosh haShono is frequently pushed off by 1-2 days, to prevent Yom Kippur falling out on a Friday or Sunday, as well as to prevent Hoshana Rabba falling out on a Shabbos, so if we didn’t have these 4 Dechiyos {which Hillel in 4118 was authorized by Toroh law to institute to push off the actual day of Rosh haShono}, then the 19 year cycle would be much closer every 19 years.