Firstly, the serial on the paperwork matches the movement and reference. The booklet matches the retailer on the paperwork so that must all be correct and original.
The only items that could realistically be in doubt are the buckle and box but they’re both period correct so no reason to think they’ve been added later.
Nice little find.
It's always hard to know what's happened to a decades old watch like this one. Its clearly had some wear and there is no reason not to think it was worn daily for years before being put in box when its owner moved on. The owner was clearly careful enough to hold on to the box and receipt, which match the watch. So I'd say there's an excellent chance that it's all original and exactly how it looks.
Great find.