Mothers exaggerate or have selective memory. My mother would read one long book or two short ones to me and she told my wife she would have to "read three books to him at lunch just to get him to eat". Maybe it took three books a couple of times, but the statement implies regularity that was not there (I remember).

Even if you knew the book at 18 months, it was likely still recitation-based, though some word recognition is possible. I think that if we tone down potential exaggeration a bit that's where you end up, which is good but not freakish.