I came across these two photos, both of 707-300s:
Photo © Johan Ljungdahl
Photo © Don Gilham
If you enlarge them, you can see the right one has an additional pair of exits just behind the wing, which the left one does not have. Why is that so? Were these an option? Or were they added on all 707-300 after a certain time?
I´d very much appreciate if someone could share some information on that "mystery".