I don't have a photo of the case back, but no, no sign of wear caused by a Nato. And I have mine for more than 13 years, now. As for my sources, here I found it from a french watch dealer who had some marvels.
80 years old, this old brother! They really had some stunning watches, at that time. This Chronograph is one of them, among many others. Do you own or know any of them? Best, Nicolas ...