I agree that many NPS rangers are quite ignorant about their sites, and history in general (this does not apply to the park historians and other staff members who are historians by education or hobby). I have heard NPS park ranger guides say some pretty outlandish things to the public, particularly about the material culture of the war. I remember one at Petersburg who was speaking to a tour group, say that there was no such thing as a rectangular Confederate battle flag - all were square.