That invoice doesn't tell a lot but your S/N is damn high. Could have been a demo unit that finally got repurposed for final sale, an acquisition from a previous owner and again - re-certified and sold to Nagra. Or they simply over built inventory and there is sat for 8 years. Back then it was common practice for big firms to lease capital equipment like testers, analysers and scopes. Could have been that too, where Nagra leased the thing for a eight years and some corporate bean-counter went "WTF", buy the damn thing ! We went through similar equipment change-overs at the company I worked for in Silicon Valley where ROI wasn't obvious at the beginning of using a piece of equipment.
Hard to tell.
But I'll tell you this ... Nagra took care of that thing. No doubt about that !