After 1799, the Census records are fairly accurate, as long as you know where they were living. If you are lucky enough to know where they were living at a given point, you can also contact the parishes directly. Under the old French Common Law, the RCC was responsible for keeping official records. Even after the French left Canada, the practice was to register every birth, marriage and death with the the Church. Some places also had concurrent civil registration (which sometimes causes discrepancies because one was married before the notary on a separate date from the Church wedding.)
Additionally, many people confuse baptismal dates with birthdates. But depending on the circumstances, especially as you get into westward expansion into remote regions, it could be 2-3 years before a priest came along by canoe who would baptize a child. Or the family might live in a Vermont lumber camp and wait until they went home in the spring to have their children baptized back in Quebec. Not every researcher is good about putting information into context...and as you've noted, many (especially on the familysearch.org site) even cite their sources. So the moral of the story is...whenever humanly possible...stick with parish records whenever available, followed by officially published civil records, then get into published works (and note that even Jette, Tanguay and Drouin don't always agree...some even confuse spouses and make leaps in logic), and finally the LDS works.
Hope all's going well for you. It sounds like you're really making a load of progress!