It’s easy to say “someone screwed up” but keep in mind that people aren’t the same. Keeping on the theme of “vampires” — Twilight vampires are very different from Interview With a Vampire vampires and both differ from the vampire as laid out in Dracula which differs from vampires of mythology. Would a vampire’s reflection show in a modern day mirror since it has no silver backing? Rhetorical, but I’m just pointing out that different developer interpretations don’t necessarily mean someone screwed up.
A clear design document (which is what they have now) doesn’t prevent mistakes, but it does make it so that there’s something to reference for consistency. Otherwise it is open to interpretation. Even if it’s only mostly correct on a go forward basis — laying out “this is how it should be” is a much better step to consistency then “well, immerse yourself in 25 years of conflicting code by multiple developers and then make a judgment call.”
In my opinion, not knowing the right answer and making a choice isn’t screwing up.