Yes, authors make mistakes.  Sometimes we forget something we have written earlier.  This is especially easy to do when we are writing a series.  Yes, I have made some mistakes in my tales of the Frog Princess.  I don't mind if you tell me about it either.  However I, like everyone else, take the criticism much more kindly if the critic is not rude.  I just received a very rude email telling me something that I had heard from dozens of my fans, all of whom had stated it in a much more polite fashion.  If you are going to be rude, I do not want to hear from you.  If you are going to be polite, please write!