Good eye.
You're right. 4 and 9 have everything identical, except for the green boom truck that has no shadowing under it. A friend sent me that story over a week ago.
Being an artist, I noticed the details right away, the people in 4 and 9 in the same position, vehicle differences, the inflatable boat, etc. Being a bit of a perfectionist, he was a little embarrassed that he sent it out to so many friends.
Good eye.