Thank you for mentioning it, though it isn't the problem.

Years ago I sold 3,500 door viewers to a college. They called a few weeks
later to say they had installed them, but they were defective; they could
see the inside of the room clearly. I told him I would get back to him.

I checked our viewers and found that while you could see into the room, it
was a dim fuzzy view of a small area; certainly not a problem. I was
telling someone about this and happened to say that it was like he had
installed them backwards. Hearing myself say it....

I called him back and explained which end faced out. He said that was
ridiculous but would get back to me. I never heard from him again.

He had installed 3,500 doorviewers backwards. So, having the blades in
backwards is not so impossible.